Toshiba Brave Lupus won both the league round-robin and the Microsoft Cup knockout competitions.

• The top 4 teams also qualified to for entry into the All-Japan Rugby Football Championship.

If teams are level at any stage, tiebreakers are applied in the following order: • Difference between points for and against • Total number of points for • Number of matches won • Aggregate number of points scored in matches between tied teams • Number of matches won excluding the first match, then the second and so on until the tie is settled The top eight teams in the league played off for the Microsoft Cup (2005) knock out tournament, which was won by Toshiba Brave Lupus.

The number of tries and goals being equal, the result was decided in favour of Yamaha by a lottery held at Hanazono after the game.

Fukuoka Sanix Bombs and Secom Rugguts won promotion to the 2005–06 Top League via the 2005 Top League Challenge Series, while Honda Heat and Toyota Industries Shuttles progressed to the promotion play-offs.