Abstract: Objectives To approach the correlation between the NO concentration and stenosis of tracheal lumens in the tracheal graft tissue,and the effect on the two factors with immunosuppressant.Methods Forty eight male normal albino rabbit were divided into group A and B,randomly and equally.Tracheal segment were allotransplanted in two groups.No immunosuppressant was given in group A,The recipients were treated with cyclophosphamide in groap B.Eight rabbits of each group were sacrificed at the third day,seventh day and fourteenth day after operation,and the NO concentration and the percent patency in these postmortem specimens were examined totally.Results Tracheal stenosis was found more serious in group A than in group B,There was significance in the difference between the seventh and fourteenth day after operation(P＜0.01).At different time(the seventh and the fourteenth day)after operation,the NO concentration in group B was significantly lower than in group A(P＜0.05).Conclusion The correlation was found between the NO concentration and stenosis of tracheal lumens in the tracheal graft tissue;Immunosuppressive drugs can reduce the production of NO,and help to relieve the tracheal stenosis after operation.