Abstract: Objective: To study the influence of N-acetylcysteine(NAC) on the growth and spontaneous metastasis of lung adenocarcinoma in T739 mice.Methods: Fifty-one T739 mice were randomly divided into 3 groups.Group Ⅰ acted as the control.Group Ⅱ and Ⅲ were administered different doses of NAC(0.5 g·kg^-1·d^-1,1.0 g·kg^-1·d^-1) in drinking water 72 hours before subcutaneous inoculation of LA795 lung adenocarcinoma cells(0.2×10⁶),and then the formation and growth of the primary tumor,the number of lung metastasis and the concentration of glutathione(GSH)were observed.Results: On the fourth day after inoculation,the incidence of tumor was 81.25% in the control group,which was much higher than that of the treatment groups(47.1%,38.9%,respectively)(P<0.05).The weight of the tumor decreased significantly(P<0.05 and P<0.01) compared with the control group.The doses of NAC was negatively related to the weight of the local tumor(P<0.01).The influence of NAC on the number of lung metastasis was not statistically significant(P>0.05).The weight of the mice decreased greatly(P<0.01) compared to the initial weight in all the groups and the difference between the 3 groups was not significant(P>0.05).Conclusions: NAC can inhibit the formation of the local tumor and has no significant side-effects on the mice.It is a promising agent.