Introduction Obstructive sleep apnea(OSA)has been suggested to be a potential contributing factor for nonalcoholic fatty liver disease(NAFLD).Studies on the association between continuous positive airway pressure(CPAP)and NAFLD in OSA patients are limited and controversial.Objectives The aim of this study was to assess the relationship between OSA and NAFLD and the effect of CPAP therapy on serum aminotransferase levels in OSA patients.Methods A total of 160 consecutive patients who underwent standard polysomnography were enrolled.Blood samples were obtained in the morning after sleep for biological profile measurements.Non-invasive ultrasound techniques were used to assess liver steatosis and fibrosis.Within the OSA group,serum aminotransferases were detected before and after CPAP treatment.Results Alanine aminotransferase(ALT),aspartate aminotransferase(AST),gamma-glutamyltransferase,and liver steatosis score increased significantly with an increase in OSA severity.Stepwise multiple regression with liver steatosis score,ALT,AST as dependent variable,respectively,apnea-hypopnea index(β = 0.447,p = 0.020; β = 0.266,p = 0.001; β = 0.351,p = 0.020,respectively)significantly predicted the liver steatosis score,ALT,AST after adjustment for confounders.After 3 months of CPAP treatment,there was a significant decrease in both ALT(54.20 ± 24.34 vs.46.52 ± 24.95,p = 0.000)and AST(31.82 ± 8.91 vs.29.00 ± 8.34,p = 0.039).Conclusions OSA severity was independently associated with liver steatosis and elevation of serum aminotransferases.3 months of CPAP therapy were associated with a statistically significant improvement on liver injury in OSA patients.