A method for manufacturing a bicycle crank is revealed. After being extended, bent and forged, an aluminum alloy pipe becomes an L-shaped part formed by a cylindrical crankshaft portion and an oval crank portion integrally connected to each other. A plug is inserted into an outer end of the crank portion while a periphery of an outer end of the crankshaft portion is punched to form a shaft-connecting portion. An assembling hole is arranged at the outer end of the crank portion, corresponding to the plug. Thus a bicycle crank is produced. Thereby not only the assembly of the bicycle crank is easier and more convenient, the structural strength of the bicycle crank is increased effectively to against vibrations and impacts. The bicycle is lightweight and the bicycle crank is more streamlined so that consumers are attracted. Thereby the market competitiveness is increased.