The aim of the current study is to find the correlated and predicting variables of O2 challenge test, a screening test for finding suitable donors for lung in brain death patients. We used brain death database of the Masih lung transplantation center. We used extracted the result of O2 challenge test along with demographic data, , cause of injury, patients’ condition and laboratory finding for analysis. For finding the correlation between test result and other variables we used Pearson correlation coefficient. We used linear regression model to find which of the mentioned variables could predict O2 challenge test results. The mean oxygen-challenge test result was 266.6 ± 85.6. The cause of brain death was trauma (66.7%), vascular aneurism (13.3%) and other causes (20%). the mean age of the patients was 30.3 ± 14.1 years. O2 challenge test results were significantly correlated with age(R=-0.351, p=0.019) and leukocyte count (R=0.315, p=0.042). After entering the variable into the regression model; serum level of Na (B= 1.489, p<0.001), age (B= -2.572, p= 0.003) and male gender (47.992, p = 0.043) were significant predictors of O2 challenge test results (R2 = 0.947, p<0.001). Our results showed that higher serum level of Na is a predictor of a better O2 challenge test results. Male gender and younger age were also predictors of better result. The cause of brain death and a history of shock did not predict the test result.