In this research, it is aimed to find out to whether family, peer and teacher support variables and demographic properties predict the high school students' career maturity levels. The sample of the study included totally 483 high school students. The data was collected by "Career Maturity Inventory", "Perceived Social Support Scale-R" and "Personal Information Questionnaire" developed by researchers. Predictors of high school students' career maturity levels were analyzed by Stepwise Regression technique. T-test was done to find out if there are any significant differences between career maturity level of girls and boys. Findings of this research were family support, gender, teacher and peer support predicted career maturity of high school students significantly. School type and grade level did not predict high school students' career maturity levels significantly. Furthermore, girls' career maturity levels are higher than boys'. The findings were discussed and suggestions were made.