Carnosine (beta-alanyl-L-histidine) was the first and the simplest example of active peptides (actually a dipeptide). The anti-ageing effect of carnosine had been demonstrated in many studies in vivo and in vitro. More recently,there were some studies verifying the effect of carnosine on preventing cataract development. The molecular mechanisms are largely undetermined. The effect of carnosine on delaying the cataract formation may be through anti-glycation of protein, antioxidative impairment, protection protein against cross-links and DNA damage. Further study of carnosine on its biological features and the mechanisms of delaying the progression of cataractogenesis may provide a new therapy for preventing cataract.