Abstract: Phenylcyclobutylamide derivatives and their optical isomers, the preparing processes and the uses thereof, which includes the compounds of formula (I), their pure stereoisomers and their pharmaceutically acceptable salts. In formula (I), R is H, formacyl, acetyl, haloacetyl, benzoyl, benzyloxy carbonyl (Cbz), t-butoxy carbonyl (Boc), or 9-fluorenyl methoxyl carbonyl (Fmoc). The present novel compounds have pharmaceutical activity and are prepared by condensation reaction of racemic, levo- or dextro-demethyl Sibutramine and racemic or D/L isoleucine under a mild condition. It is demonstrated that the present compounds have effect of losing weight to obese mode rats in different level and the effect is better than Sibutramine by the animal experiments. So the medicaments prepared by the present compounds or the medicaments prepared by the compositions of the present compounds and other pharmaceutical activity compounds may be used for treating obesity.