The research was planned as a descriptive study of factors affecting fatigue in adolescents. 1031 adolescents participated in this study. Research data was collected from students who attended classes in preparation for the University. 'Personal data form' and 'Chalder fatigue scale' and 'Epworth Sleepiness Scale' were used as data collection tools. Data obtained in SPSS 23 environment, first of all, lost data was checked for extreme values, normality and homogeneity were tested. The research model was tested by structural equality modeling. Revised model estimating factors affecting adolescent fatigue and goodness of fit values were determined as χ2 = 286.66, χ2/DF = 4.70, NFI = 0.86, TLI = 0.86, CFI = 0.89, GFI = 0.96, AGFI = 0.94, RMSEA = 0.06, RMR = 0.70. Number of siblings (t = -2.693; p < 0.05), and adolescent sleepiness (t = 7.550; p < 0.001) were found to have a significant effect on fatigue. Age, maternal education level and paternal education level were found to be ineffective on fatigue. It was determined that sleepiness was the most important factor on adolescent fatigue. Various suggestions have been made in accordance with the acquired results.