Suspension for a bicycle comprising an elastic element and a blocking/releasing device of the elastic element, wherein the blocking/releasing device comprises: - a closed hydraulic circuit containing a working fluid; - a cylinder-piston assembly comprising a cylinder and a piston slidable in said cylinder, said cylinder-piston assembly being inserted in the hydraulic circuit and being disposed operatively in parallel to said elastic element; - a valve configurable according to an open configuration, such that the working fluid freely flows in the hydraulic circuit for enabling movements of the piston inside the cylinder, and a closed configuration, such that the working fluid is prevented from flowing in the hydraulic circuit and the piston is kept blocked by the working fluid, wherein the blocking/releasing device further comprises a main housing receiving inside the cylinder-piston assembly, wherein the hydraulic circuit is made in a space formed between the walls of the main housing and the walls of the cylinder, said main housing being coupled to said elastic element on a first side of the latter, wherein the piston comprises a stem projecting from the cylinder and from the main housing and is connected to the elastic element on a second side of the latter opposite to the first one, characterized in that the valve is commanded by an actuator inserted in the hydraulic circuit, wherein said actuator comprises an electric motor communicating with the valve by a hydraulic transmission, said electric motor comprising a linearly movable shaft acting on said hydraulic transmission by a membrane fluidically separating the electric motor from the hydraulic transmission. - a closed hydraulic circuit containing a working fluid; - a cylinder-piston assembly comprising a cylinder and a piston slidable in said cylinder, said cylinder-piston assembly being inserted in the hydraulic circuit and being disposed operatively in parallel to said elastic element; - a valve configurable according to an open configuration, such that the working fluid freely flows in the hydraulic circuit for enabling movements of the piston inside the cylinder, and a closed configuration, such that the working fluid is prevented from flowing in the hydraulic circuit and the piston is kept blocked by the working fluid, wherein the blocking/releasing device further comprises a main housing receiving inside the cylinder-piston assembly, wherein the hydraulic circuit is made in a space formed between the walls of the main housing and the walls of the cylinder, said main housing being coupled to said elastic element on a first side of the latter, wherein the piston comprises a stem projecting from the cylinder and from the main housing and is connected to the elastic element on a second side of the latter opposite to the first one, characterized in that the valve is commanded by an actuator inserted in the hydraulic circuit, wherein said actuator comprises an electric motor communicating with the valve by a hydraulic transmission, said electric motor comprising a linearly movable shaft acting on said hydraulic transmission by a membrane fluidically separating the electric motor from the hydraulic transmission.