Monster Farm Online(also known as Monster Rancher Online) is the first game in the Monster Rancher series for the PC, as well as being the first MMORPG in the series. The game is only available in Japanese. The game was originally scheduled for winter 2006, but was postponed to December 21, 2007. Registration and download were closed off again and will reopen November 2009, as the official site`s FAQ stated.

Like other games in the series, the main gameplay aspect is raising, and fighting with monsters.