A variable speed motor building block is applicable to connection with a peripheral building block group and comprises a housing, a speed change unit and a motor for driving the speed change unit. The housing comprises a hollow containing chamber. The speed change unit is contained in the containing chamber and comprises a plurality of maneuvering gear sets that are detachably arranged; each maneuvering gear set is provided with a first gear and a second gear linked with the first gear; each first gear has a first number of teeth; each second gear has a second number of teeth; each first number of teeth is greater than each second number of teeth; one of the first gear and the second gear of each maneuvering gear set is engaged with the other one of the first gear and the second gear of each adjacent maneuvering gear set. With the adoption of the maneuvering gear sets with identical gear specifications, the adjacent maneuvering gear sets are engaged and matched simply; a user can perform combination to form various different configurations to generate different speed change ratios.