The invention deals with an eccentric gearbox with selectable large speed ratio.In this gearbox many eccentric gear pairs (1,4),(2,5) and (3,6) are assembled in parallel, and are connected to a common input shaft and a common output shaft.In every gear pair, one gear keeps its orientation fixed is called as fixed gear and another gear that rotates about its own axis is called as moving gear. Difference in number of teeth on the two gears of an eccentric gear pair is kept to one tooth or more.Through proper selection of a particular gear pair any speed ratio can be selected. In this way, it is possible to make a compact gearbox,with multiple large speed ratios.Such a gear box can be used in automobiles, robot manipulators, earth moving equipments, space applications, toys, hand held tools and in many other applications.