New asymmetric hollow fiber reverse osmosis (RO) membrane was developed from a new chlorine-resistant copolyamide [4T-PIP(30)] with a piperazine moiety by a conventional phase-separation method. The new 4T-PIP(30) hollow fiber membrane has the same low-pressure RO performance as cellulose triacetate hollow fiber membrane (FR = 205 L/m(2) day, Rj = 99.6%) and superior chlorine resistance as well as pH resistance to conventional aramid RO membranes. Structural analysis and viscoelastic study revealed that the new hollow fiber consisted of a top skin, dense layer, and microporous layer, and that it began to decrease its elasticity at 80 degreesC in water, which is possibly related to its good and stable RO performance around room temperature. Several kinds of RO modules were made from the new hollow fiber membranes, for which RO performances were stable for 2 years in chlorinated feed water desalination (the free residual chlorine ranged from 0.1 to 1.1 mg/L).