The aim of this study was to examine the relationship between personality traits, procrastination and school success on high school students and to examine the possibility of predicting school success through personality traits and procrastination. Research is conducted on convenient sample of N = 222 participants, male and female high school students of second, third and fourth grade of two high schools. Instruments used for examination of these constructs are Tuckman Procrastination Scale and Big Five Inventory that measures Extraversion, Neuroticism, Conscientiousness, Agreeableness and Openness. Students' grade point average and grades from Croatian language, math and first foreign language were used as a measure of school success. The results of this study indicate that Conscientiousness is in a positive correlation with GPA and grade from Croatian language, while Extraversion and Agreeableness are in a negative correlation with grade from first foreign language. Furthermore, it was shown that procrastination has a negative correlation with GPA and grade from Croatian language and there is no relationship between procrastination and grades from math and first foreign language. Also, the results showed that procrastination is in a negative correlation with Neuroticism and in a positive correlation with Conscientiousness, Agreeableness and Extraversion, while there is no relationship between Openness and procrastination. Finally, it has been shown that Conscientiousness and Neuroticism were positive predictors of GPA and grade from Croatian language. Openness is a positive predictor of grade from first foreign language, while Extraversion and Agreeableness are negative predictors. None of the variables have shown statistically significant correlation with the math grade or was a predictor of this criterion.