The utility model relates to a bicycle brake which realizes braking of the bicycle via a hydraulic structure. The hydraulic brake for bicycles comprises a driving hydraulic oil cylinder device which is arranged on a bicycle head, driven hydraulic oil cylinder devices which are symmetrically arranged at both sides of a bicycle rim, and a connection oil circuit of the two devices. The hydraulic brake for bicycles is characterized in that each driven hydraulic oil cylinder device comprises a cylinder body, a piston in the cylinder body and drag friction blocks which are fixed on the outer end of the piston; the other end of the piston is sheathed with a hat type seal ring, and the seal performance is perfected. The main power of the driving hydraulic oil cylinder device is fully utilized, the mechanical structure is simplified, and the mechanical performance is provided. The hydraulic brake for bicycles has the advantages of simple structure, sensitive brake effect and good control performance.