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 . <EOS>