This is a list of number ones on the Billboard Japan Hot 100 chart in 2008.
| Issue date | Song | Artist | |
|---|---|---|---|
| January 21 | "Stay Gold" | Hikaru Utada | |
| January 28 | "Be Free" | Greeeen | |
| February 4 | "Deai no Kakera" | Ketsumeishi | |
| February 11 | "Soba ni Iru ne" | Thelma Aoyama featuring SoulJa | |
| February 18 | "Lips" | KAT-TUN | |
| February 25 | "Anata ga Koko ni Itara" | Porno Graffitti | |
| March 3 | "Step and Go" | Arashi | |
| March 10 | "Taiyō no Namida" | NEWS | |
| March 17 | "Sono Mama" | SMAP | |
| March 24 | "Wahaha" | Kanjani Eight | |
| March 31 | "Fight the Blues" | Hikaru Utada | |
| April 7 | "New Look" | Namie Amuro | |
| April 14 | "Kurikaesu Haru" | 244 Endli-x | |
| April 21 | "Shuchishin" | Shuchishin | |
| April 28 | "Burn (Fumetsu no Face)" | B'z | |
| May 5 | "Bleeding Love" | Leona Lewis | |
| May 12 | "No More" | Tsukasa Maizu | |
| May 19 | "Summer Time" | NEWS | |
| May 26 | "Don't U Ever Stop" | KAT-TUN | |
| June 2 | "Dreams Come True" | Hey! Say! JUMP | |
| June 9 | "Kiseki" | Greeeen | |
| June 16 | |||
| June 23 | "Verb" | Glay | |
| June 30 | "Ai Ai Gasa" | Tegomass | |
| July 7 | "One Love" | Arashi | |
| July 14 | "Summer Song" | Yui | |
| July 21 | "Love the World" | Perfume | |
| July 28 | "Make My Day" | Yui Aragaki | |
| August 4 | "Your Seed" | Hey! Say | JUMP |
| August 11 | "Gift" | Mr. Children | |
| August 18 | "I Am Your Singer" | Southern All Stars | |
| August 25 | "Kono Toki Kitto Yume Jya Nai" | SMAP | |
| September 1 | "Truth" | Arashi | |
| September 8 | "Secret Code" | KinKi Kids | |
| September 15 | "Hanabi" | Mr. Children | |
| September 22 | |||
| September 29 | "Tegami (Haikei Jūgo no Kimi e)" | Angela Aki | |
| October 6 | "The Birthday: Ti Amo" | Exile | |
| October 13 | "Happy Birthday" | NEWS | |
| October 20 | "Love,too Death,too" | Porno Graffitti | |
| October 27 | "Akai Ito" | Yui Aragaki | |
| November 3 | "Mayonaka no Shadow Boy" | Hey! Say | JUMP |
| November 10 | "Musekinin Hero" | Kanjani Eight | |
| November 17 | "Beautiful Days" | Arashi | |
| November 24 | "Tsuretette Tsuretette" | Dreams Come True | |
| December 1 | "Hakanaku mo Towa no Kanashi" | Uverworld | |
| December 8 | "Last Christmas" | Exile | |
| December 15 | "White X'mas" | KAT-TUN | |
| December 22 | "Yowamushi Santa" | Shuchishin | |
| December 29 | "Days" | Ayumi Hamasaki |