An object of the present invention is to provide a modified cyclic aliphatic polyamine having a low viscosity and a small content of unreacted polyamine which can provide, when it is used as a curing agent for epoxy resin, an epoxy resin composition having an improved workability without adding solvent or diluent and an excellent property of epoxy resin cure product. The above modified cyclic aliphatic polyamine is obtained by addition reaction of a cyclic aliphatic polyamine such as isophoronediamine and norbornanediamine and an alkenyl compound such as styrene. The modified cyclic aliphatic polyamine thus obtained is added in epoxy resin to be used as a curing agent for epoxy resin.