1999 was the year in which Fukuda Asuka graduated from Morning Musume and Hello! Project; Goto Maki joined Morning Musume; Taiyou to Ciscomoon, Coconuts Musume, Country Musume, and Melon Kinenbi were formed; Miyoshi Chinatsu joined Hello! Project; Yanagihara Hiromi died in a car crash; and Kobayashi Azusa left Country Musume and Hello! Project.
- February 21: Taiyou to Ciscomoon is formed.
- March ?: Coconuts Musume is formed.
- April 1: Hello! becomes Hello! Project.
- April 18: Fukuda Asuka graduates Morning Musume and Hello! Project.
- April 27: Country Musume is formed.
- May 11: Miyoshi Chinatsu joins Hello! Project.
- July 16: Yanagihara Hiromi dies in a car accident.
- August 10: Melon Kinenbi is formed.
- August 22: Goto Maki joins Morning Musume as the 3rd generation.
- August 23: Kobayashi Azusa leaves Country Musume and Hello! Project.
- October 3: Petitmoni is formed.
- January 14: Mogi Minami is born.
- February 15: Ogata Haruna is born.
- February 25: Ichioka Reina is born.
- March 4: Fujii Rio is born.
- March 12: Oda Sakura is born.
- March 14: Yokogawa Yumei is born.
- March 26: Aikawa Maho is born.
- May 7: Sato Masaki is born.
- May 31: Shimano Momoko is born.
- July 7: Kawamura Ayano is born.
- August 4: Hirose Ayaka is born.
- August 29: Mashiro Kana is born.
- September 22: Yoshihashi Kurumi is born.
- October 7: Nonaka Miki is born.
- October 20: Niinuma Kisora is born.
- October 24: Kamikokuryo Moe is born.
- October 27: Kudo Haruka is born.
- November 10: Tanabe Nanami is born.
- November 30: Kaga Kaede is born.
- December 11: Hirai Miyo is born.
- February 10:
- March 10: Motto - Tanpopo
- April 21: Tsuki to Taiyou - Taiyou to Ciscomoon (debut)
- May 12: Manatsu no Kousen - Morning Musume
- June 9: Junjou Koushinkyoku - Nakazawa Yuko
- June 16: Tanpopo (Single Version) - Tanpopo
- June 23: Gatamekira - Taiyou to Ciscomoon
- July 14: Furusato - Morning Musume
- July 23:
- July 28:
- August 4 - Unchain My Heart - Miyoshi Chinatsu (debut)
- August 25:
- September 9 - LOVE Machine - Morning Musume
- September 29 - Magic of Love - Taiyou to Ciscomoon
- October 20 - Seinaru Kane ga Hibiku Yoru - Tanpopo
- November 10 - Love, Yes I do! - Miyoshi Chinatsu
- November 25 - Chokotto LOVE - Petitmoni (debut)
- November 30 - Yukigeshiki - Country Musume
- December 8 - Marui Taiyou -winter ver.- - Taiyou to Ciscomoon
- March 31: TANPOPO 1 - Tanpopo (debut)
- July 28: Second Morning - Morning Musume
- October 27: Taiyo & Ciscomoon 1 - Taiyou to Ciscomoon (debut)
- January 28: Morning Musume's major debut 1st anniversary
- September 14: Morning Musume's formation 2nd anniversary
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