The invention provides an electric power assisted bicycle and an assembly suitable for the electric power assisted bicycle and capable of being mounted on a bicycle frame. The assembly not only can simplify an auxiliary power mechanism used for the electric power assisted bicycle but also can be easily mounted on the bicycle frame. The assembly is characterized in that at least the following components are arranged on a common base to form the assembly: a chain wheel, an electric power output mechanism, an auxiliary gear, a connecting mechanism and a drive shaft, wherein the chain wheel is used for transmitting pedaling force to a drive wheel and can rotate; the electric power output mechanism outputs electric power used for assisting the pedaling force through an output shaft; the auxiliary gear is connected with the output shaft of the electric power output mechanism through a gear mechanism; the connecting mechanism connects the auxiliary gear with the chain wheel coaxially; the drive shaft is stored in a shaft sleeve in a rotating mode by utilizing the pedaling force; the shaft sleeve is connected with the common base, or the shaft sleeve and the common base are formed integrally.