The present research aims to compare the cognitive performance of the adolescents suffering from MDD and PTSD in the working memory and information processing. the selected sample in this casual-comparative study included 15 MDD patients, 15 youth PTSD subjects and 15 normal subjects who were matched by age, IQ, sex as well as social and economic status variables. The tool package employed in this investigation comprised child depression inventory (CDI), State-Trait Anxiety Inventory, Impact of Event Scale (IES-R), Wechsler’s Memory and Intelligence Test, and The Information Processing Index Test. Findings were analyzed using the ANOVA, MANOVA analysis statistical method.as indicated by our result, in the verbal memory there is a significant difference between groups of depression and PTSD and between depressed and normal subjects. in the reverse spatial working memory there are significant differences between normal and PTSD. in the visual memory and information processing, the significant difference is between normal and both PTSD and depressed.The findings of this study confirm the disorders of working memory and speed of information processing in adolescents with depression and post-traumatic stress disorder.