Creatine is alleged to be a popular nutrition to enhance sports performance.It can be metabolized to methylamine, which is further converted to formaldehyde, hydrogen peroxide and ammonium by semicarbazied-sensitive amine oxidases (SSAO).Recently, the safety of chronic creatine administration has caused serious concern.It is proposed that supplementation of creatine could increase the methylamine levels.As the physiological substrates of SSAO, the enhancement of methylamine may cause the increase of SSAO activity.Increases in SSAO activity are linked to vascular disorders associated with pathological conditions such as diabetic complications, heart failure, and vascular dementia.The relationship between the potential toxicity of chronic creatine administration and SSAO activity is necessary to be discussed.