A high-hydration contact lens having a high strength is disclosed which is made of a copolymer composed of (i) 40 to 90 wt. % of N,N-dimethyl acrylamide, (ii) 5 to 50 wt. % of a hydrophobic monomer, (iii) 0.1 to 10 wt. % of an unsaturated carboxylic acid having one ethylenically unsaturated bond, and (iv) 0.01 to 5.0 wt. % of a crosslinking agent, wherein the hydrophobic monomer is selected from the group consisting of phenyl acrylates, benzyl acrylates, phenyl methacrylates, benzyl methacrylates, alkyl acrylates, alkyl methacrylates, cyclohexyl acrylates and cyclohexyl methacrylates, and the crosslinking agent is selected from those represented by formula (I), (II), or (III) ##STR1## wherein X represents a hydrogen atom or a methyl group, a is an integer of 2 to 23, and b and c each is an integer of 2 to 14.