Alien Nine (エイリアン9, Eirian Nain) is a Japanese manga series written and illustrated by Hitoshi Tomizawa. The manga was serialized in Akita Shoten's Young Champion magazine from June 1998 to August 1999, spanning 3 tankōbon volumes. In 2003, Tomizawa released a 1-volume sequel to the series called Alien 9 Emulators. In 2015, Tomizawa also released a sequel doujinshi to Alien 9 and Alien 9 Emulators called Alien 9 Next. Both the manga and anime are noted for their moe art style and heavy violence despite the young main characters, Pokémon-like monster designs, and initial appearances of a slice-of-life-esque series.

It was adapted into an original video animation (OVA) series by J.C.Staff between June 2001 to February 2002. The English adaptation of the series was first licensed by Central Park Media, and has played on Comcast's Anime Selects. Central Park Media released the title under their "US Manga Corps" line, on a single DVD, and later re-released the DVD in a box set with all three manga volumes, which was also licensed by Central Park Media under their "CPM Manga" line. Central Park Media filed for bankruptcy in 2009, and the DVDs and manga volumes subsequently went out of print in North America.