The fourth season of Winx Club premiered in Italy on Rai 2 on April 15, 2009, and concluded its run on November 13, 2009. It premiered on Nickelodeon US, advertised as Winx Club: The Power of Believix, on May 6, 2012, and concluded its run on July 29, 2012.
In an interview with Iginio Straffi from before the fourth season's premiere, it was revealed that the season would introduce a new fairy. Straffi listed the novelties of the upcoming season, including the revelation that the main characters would "find a seventh fairy" on Earth. On the same day, a Rai Due press release announced Roxy's role in the new season, saying that the fairies "will meet Roxy, a new character who will become part of the close-knit Winx group. She is a rebellious and determined girl who will discover that she is the Fairy of Animals, and at the same time, the last fairy on Earth."
This is the last season of the show's original run. As a result, it was the last season dubbed by Cinélume in English, and the last season to be produced in Italian first. After the American company Viacom became a co-owner of Rainbow in 2011, all later seasons were produced in English first.
“The Winx Club is back! Now they will have to reach the Believix level, a new transformation that grant the ability to make someone believe in magic. In addition, Believix also gives 3 additional wings to make the form more powerful: Speedix (speed enhancement), Zoomix (teletransportation), and Tracix (time traveling). They will also meet the Wizards of the Black Circle, a group of villains who are after the last fairy on Earth, in order to gain full power. Winx Club will have to find her protect her from the the Wizards, but they have to go unnoticed. In order to live on Earth, they will open a pet shop named Love & Pet and meet Roxy, a girl who works at the Frutti Music Bar. Soon they will find out that Roxy is the last fairy on Earth! In the process, Roxy is able to discover her powers, and believing in herself and in Winx Club, will turn into a fairy and will help Winx Club drive away the Wizards and rescue the imprisoned fairies. However, they now have to face the fairies of Earth and their Queen Morgana, who are seeking revenge on humans for not having believed in them: this has made them weaker and they have been imprisoned by the Wizards. Winx Club are forced into an uneasy alliance with the Wizards as they now race to save humanity. Will the Winx Club prevail?”
- The Fairy Hunters
- The Tree of Life
- The Last Fairy on Earth
- Love & Pet
- Mitzi's Present
- A Fairy in Danger
- Winx Believix
- The White Circle
- Musa's Song
- Winx Club Forever!
- Dad! I'm a Fairy!
- The Wizards' Attack
- 7: The Perfect Number
- Magic Lessons
- A Virtual World
- The Enchanted Island
- The Nature Rage
- In Diana's Kingdom
- The Gifts of Destiny
- Sibylla's Cave
- The Frozen Tower
- Bloom's Trial
- The Day of Justice
- Morgana's Secret
- Ice and Fire
- Nickelodeon did a one hour episode for the premiere of the season, combining the first two episodes of the season.
- Nickelodeon aired two back-to-back episodes every Sunday.
- This is the last season to be dubbed by Cinélume.
- In the Cinélume dub, Angela Galluppo replaces Helena Evangeliou as the voice of Bloom.
- Several scenes in the opening resemble those of anime:
- This is the first season to use flash animation and digital ink, with it being used periodically in the first six episodes and reverting to hand-drawn animation with digital ink for the rest of the season.
- This is the last season to use hand-drawn animation.
- This is also the last season to be in a 4:3 aspect ratio (SD).
- This is the first season in which the Winx earn multiple Fairy Forms, with the second being Season 5, the third being Season 6, and the fourth being Season 7.
- This is also the first and only of these seasons in which the Winx earn three Fairy Forms.
- In one of the original versions of the plot of the fourth season, the Winx had to cope with using dark magic to fight the Wizards of the Black Circle, however they later abandoned this idea.
- In the Nickelodeon remake of the opening, Winx, You're Magic Now, some of the scenes from the original Winx Are Back are absent. In the scene of the fairies being introduced in a line, Morgana and the Major Fairies are absent.
- This is likely due to the opening being sped up a little bit and the line scene being slowed down.
- This is the first (and so far only) season where the Trix do not appear physically.