The Manga Koushien has been hosted by the city of Kouchi since 1992. This year 295 schools from 46 prefectures entered the competition.
Source: Mainichi Shimbun
A small update on Kodansha's International Manga Competition. Kodansha IMC's Ceena reminds us that although the deadline for the competition was on May 31 2007, Kodansha will accept your work as long as it's postmarked by the deadline:
AnimeOnDVD has announced a new MPD Psycho Contest:
Currently a majority of the original Chinese manga are composed of 4-panel comics and short stories. To promote original story-oriented manga, Zhejiang Gongshang University's Japanese Anime and Manga Cultural Research Group has organized the 1st Story-Oriented Original Manga Competition.
The competition, supported by Shueisha and many Chinese anime news websites and media, accepts any original manga between 10-45 pages long. The deadline is September 9th, winners will be announced in October.
Tokyopop has announced a Twelve Kingdom contest, the award is a free copy of The Twelve Kingdoms: Sea of Shadow volume 1 and volume 1 of the Twelve Kingdom anime DVD:
Nihon Ki-in (Japanese Go Association) and the Go Shogi Life Corporation has announced a new event called the "Go Original Manga Grand Prize." The award accepts any manga that focus on the amusement and depth of the game Go. The winner of the grand prize will receive 1 million yen, and the winning work will be released as a tankoubon. The deadline is November 2007, the winners will be announced in March 2008.
Source: Manga Jouhou