2003 was the year when Fujimoto Miki,Kamei Eri, Michishige Sayumi and Tanaka Reina joined as the 6th generation of Morning Musume, Yasuda Kei graduated from Morning Musume, Miyoshi Erika joined Hello! Project & Saito Miuna joined Country Musume
Members
- January 7: Fujimoto Miki joins Morning Musume
- January 19: Kamei Eri, Michishige Sayumi and Tanaka Reina join Morning Musume as 6th generation members
- March 29: Minimoni shifts: Yaguchi Mari graduates, Mika Todd becomes the new leader, Takahashi Ai becomes the new fourth member
- May 7: Yasuda Kei graduates from Morning Musume
- ???
- Saito Miuna joins Country Musume
- Miyoshi Erika joins Hello! Project
- Morning Musume Sakura Gumi and Morning Musume Otome Gumi are formed
- Aa! is formed
- ZYX is formed
Singles
- January 29: Akai Freesia - Melon Kinenbi
- February 5: Boogie Train '03 - Fujimoto Miki
- February 19: Morning Musume no Hyokkori Hyoutanjima - Morning Musume
- March 12: Ne~e? - Matsuura Aya
- March 19:
- April 9: Rock n' Roll Kenchoushozaichi ~Oboechaina Series!~ - Minimoni
- April 23: AS FOR ONE DAY - Morning Musume
- May 1:
- Haha to Musume no Duet Song - Abe Natsumi and Yosumi Keiko
- Zutto Zutto - Ichii Sayaka in CUBIC-CROSS
- May 8: Chance of LOVE - Melon Kinenbi
- May 14: Minimoni Kazoe Uta ~Ofuro Version~ / Minimoni Kazoe Uta ~Date Version~ - Minimoni
- May 21: GET ALONG WITH YOU - Nakazawa Yuko
- June 4: GOOD BYE Natsuo - Matsuura Aya
- June 18: Scramble - Goto Maki
- July 9: Kowarenai Ai ga Hoshii no / GET UP! Rapper / BE ALL RIGHT! - SALT5, 7AIR, 11WATER
- July 16: Tokyo Kirigirisu - Maeda Yuki
- July 24: Uwaki na Honey Pie - Country Musume ni Konno to Fujimoto
- July 30: Shabondama - Morning Musume
- August 6: Iku ZYX! FLY HIGH - ZYX (debut)
- August 13: 22sai no Watashi - Abe Natsumi
- August 20: SEXY NIGHT ~Wasurerarenai Kare~ - ROMANS
- August 27: Daite yo! PLEASE GO ON - Goto Maki
- September 3: 4U ~Hitasura~ - Ichii Sayaka
- September 10: MI DA RA Matenrou - Melon Kinenbi
- September 18:
- September 26: THE LAST NIGHT - Matsuura Aya
- October 16: CRAZY ABOUT YOU - Minimoni
- October 29: FIRST KISS - Aa!
- November 6: Go Girl ~Koi no Victory~ - Morning Musume
- November 12: Senpai ~LOVE AGAIN~ - Country Musume ni Konno to Fujimoto
- November 19: Mirakururun Grand Purin! / Pi~hyara Kouta - Abe Natsumi and Minimoni
- November 27: Genshoku GAL Hade ni Yukube! - Goto Maki
- December 3: Kawaii Kare - Melon Kinenbi
- December 10: Shiroi TOKYO - ZYX
Albums
- January 29: T・W・O - Matsuura Aya
- February 5: Makking GOLD 1 - Goto Maki
- February 14: Koinu Dan no Monogatari Original Soundtrack - V.A.
- February 26: MIKI 1 - Fujimoto Miki (debut)
- March 12: 1st Anniversary - Melon Kinenbi (debut)
- March 26: No.5 - Morning Musume
- April 23: Os Avrio ~Ai wa Matte Kurenai~ - Iida Kaori (debut)
- October 22: Paradinome ~Koi ni Mi wo Yudanete~ - Iida Kaori
- November 21: Sweet talk Gēn wǒ Shuō - Ruru
- December 17: Petit Best 4 - Hello! Project