Fantasy Zone is a 1986 horizontally scrolling shooter video game developed and published by Sega for arcades. It is the first game in the Fantasy Zone series, and was later ported to several home consoles, including Sega's Master System. The player controls a sentient spaceship named Opa-Opa who fights an enemy invasion in the titular group of planets. The game contains a number of features atypical of the traditional scrolling shooter. The main character, Opa-Opa, is sometimes referred to as Sega's first mascot character.

The game's design and main character have similarities to Konami's TwinBee, and both games are credited with establishing the cute 'em up subgenre. Fantasy Zone also popularized the concept of a boss rush, a stage where the player faces multiple previous bosses again in succession. The game was followed by several sequels, beginning with Fantasy Zone II: The Tears of Opa-Opa in 1987.

In the game, the player's ship is placed in a level with a number of bases to destroy. When all the bases are gone, the stage boss appears, who must be defeated in order to move on to the next stage. There are eight stages, and in all of them, except the final one, the scrolling camera is not fixed; the player can move either left or right, although the stage loops. The final level consists of a rematch against all of the previous bosses in succession before facing the final boss.

Opa-Opa uses two different attacks: the standard weapon (initially bullets) and bombs. He can also move down to land on the ground by sprouting feet and walking around until he flies again.

It is possible to upgrade Opa-Opa's weapons, get bombs and flying engine to increase speed, and get extra lives. To do these, the player must get money by defeating enemies, bases or bosses, and access a shop by touching a marked balloon. Prices rise with each purchase. When the player chooses to exit or the time runs up, another screen appears to equip these upgrades; only one engine, weapon and bomb can be equipped at a time.

Some of the purchasable weapons have a time limit that starts as soon as the shop is left. Some of the bombs can be used at any moment, but are limited in quantity. Engine upgrades are permanent. The powerups can also be reassigned by reentering the shop or touch a balloon with the word "Select" written on it. If the player loses a life, all of the upgrades are lost.

Fantasy Zone was ported to the Master System, MSX, Famicom/Nintendo Entertainment System, X68000, and PC Engine—all with similar gameplay, though with some notable differences. For example, the Master System version lacks some features such as the radar that indicates the location of the bases or a gauge that indicates energy level, and two of the bosses were replaced by alternate bosses.

Two different versions were released for the Famicom and NES. The Japanese version was released in 1987, developed and published by Sunsoft. The American version was released in 1990, developed by Pixel and published by Tengen. In 1997, Fantasy Zone was released in the Sega Ages series in Japan for the Sega Saturn.