Galaxy Fighter is a vertically-scrolling space shooter. Many kinds of enemies appear in waves to attack the player, piloting an advanced fighter ship. When destroyed, enemies will sometimes drop power-up items, which include firepower upgrades and three different types of sub weapon: small homing missiles, large forward-firing missiles, and a rotating shield that damages nearby enemies. Every so often, a large boss enemy will appear, which must be destroyed in order to proceed. Similar to Toaplan's Truxton, there are no breaks between stages, the entire game scrolls continuously forward, only interrupted when the player's ship is destroyed.