Objective To investigate the expression of neural-nitric oxide synthase (nNOS) in renal clear cell carcinoma and its clinical significance.Methods The expression of nNOS mRNA in 533 samples of TCGA database was analyzed with Student t test,and statistical analysis was performed to assess the relationship between nNOS expression and clinical prognosis with Kapla-Meier test.Western blot analysis of nNOS protein expression in 10 cases of clear cell renal cell carcinoma(ccRCC) from department of urology of Wuhan union hospital with student t test.Results The mRNA levels of nNOS in 72 cases of ccRCC in tumor tissues and adjacent tissues and were 2.99 ± 0.28 and-1.57 ± 0.17,it is significantly lower than those in adjacent tissues (P ＜ 0.01).The mRNA levels of nNOS in 533 cases of ccRCC,in tumor tissues and adjacent tissues and were 2.99 ± 0.28 and-1.76 ± 0.05,it is significantly lower than those in adjacent tissues (P ＜ 0.01).A total of 533 sample studies showed a low correlation between nNOS expression and clinical T stage,T1-1.59 ±0.08,T2-1.96 ±0.13,T3-1.90 ±0.09,T4-2.38 ±0.28 (P =0.0029) and -1.63 ±0.06 and-2.16 ± 0.13 between non-metastasis and no-metastasis (P =0.0009),and-1.57 ± 0.08 and-2.03 ± 0.11 between non-recurrence and recurrence (P =0.008).Survival analysis showed that the overall survival time were (40.3 ± 5.6) months and (48.3 ± 5.7) months in lower and higher nNOS expression,and disease free survival time were (37.1 ± 2.1) months and (40.3 ± 5.6) months in lower and higher nNOS expression,both with shorter time in low expression of nNOS (P ＜ 0.01).nNOS proteins were 1.02 ± 0.16 and 0.61 ± 0.1 1 in tumor tissues and adjacent tissues with significantly lower expression(P＜0.05).Conclusions The mRNA and protein of nNOS are lower in ccRCC with a poor prognosis of ccRCC.