Abstract: Muscle-derived neurotrophins(NTs) play important roles in the development of neuromuscular junction(NMJ).In this study,3-week-old male Sprague-Dawley rats had undergone activity-enhancing(treadmill-running) and activity-reducing(tail-suspension) respectively to discuss the characteristics of neurotrophins concentrations in growth phase as well as the effects of activities.Resultsshowed that NT-3 and BDNF presented peak concentrations in 3⁴ weeks and 5⁸ weeks after birth,which illuminated that they throw great effects on NMJ development both in early stage after birth and adolescence.The concentration of NT-4 was affected by activity-changing and had no relationship with age-changing,which suggested that it was related mainly to neuromuscular reliant function development.It was also approved that exercises could improve the concentrations of NT-4 as well as that of NT-3and BDNF in early stage after birth,which supported that training could promote the development of NMJ in growth stage.