Purpose: NAG and fructose levels are contributed to discriminating obstructive and nonobstructive azoospermia in Chinese patients, while theirsensitivity and specificity are not very satisfactory.Meanwhile,whetherNAG and fructose levels are helpful for distinguishing the histological types in patients with nonobstructive azoospermia remains elusive.Materials and methods: This study enrolled 206 cases of patients with obstructive azoospermia and 353 cases of patients with nonobstructive azoospermia.All patients underwent testicular biopsy.The study was performed between January 2008 and December 2014.Semen samples were collected by sterile plastic vessels after 3-7 days of sexual abstinence.The levels of NAG and fructose in seminal plasma were tested by commercially commercial available test kits.All testis tissues were stained by hematoxylin and eosin (HE).Results: The levels of NAG and fructose in patients with non-obstructive azoospermiawere significantly higher compared with those with obstructive azoospermia.Meanwhile, NAG positively correlated with fructosein patients with obstructive azoospermia and nonobstructive azoospermia.In patients with non-obstructive azoospermia, increased levels of NAG andfructose were observed in severe hyperspermatogenesis, Sertoli-cell-only (SCO) syndrome and maturation arrest.According tothe reference value of NAG and fructose (WHO, 1999),the results shown that NAG level was 77.7% sensitive and 44.2% specific in identifying obstructive azoospermia, and Fructose level was 46.6% sensitive and 67.4% specific in identifying obstructive azoospermia.Low level of NAG was observed in 77.2% of patients withobstructive azoospermia,which was significantly higher than those with nonobstructive azoospermia (55.8%).Also, low level of fructose was observed in46.6% of patients with obstructive azoospermia, which is obviously higher than those with nonobstructive azoospermia (32.6%).However,only a small proportion of patients with SCO syndrome, severe adverse spermatogenesis and maturation arrest exhibited lower levels of NAG and fructose.Conclusions: NAG and fructose levels are contributed to discriminating obstructive and nonobstructive azoospermia in Chinese patients, and alsohelpful for distinguishing the histological types of testes.