The present invention discloses a guava leaf extract capable of inhibiting protein tyrosine phosphotase-1b. The guava leaf extract is a water soluble extract obtained from guava leaves, and has a hypoglycemic efficacy in vivo.本發明係揭露一種抑制蛋白質酪胺酸磷酸酶-1b之芭樂葉萃取物,其為利用不同的萃取方法萃取一芭樂葉而得的水溶性萃取物,且其具有降血糖之功效。