Smartphones have become an essential part of daily life. Smartphones and related mobile technologies have the potential to affect a wide range of cognitive domains. This reduces an individual’s social implication in the real world and, as a consequence, his or her psychological well-being. Purposes: This study aimed to evaluate the cognitive functions including attention, memory, logical reasoning and visual processing in adolescents who use smartphones and to determine the difference between no-risk and high-risk smartphone users in cognitive functions. Methods: Two hundred ninety two normal adolescents from both sexes participated in this study, Their age ranged from 12-16 years. They were divided into two groups according to the score of smartphone addiction scale. Group A included no-risk smartphone users and group B included high-risk smartphone users. Assessment of cognitive functions was conducted by assessed by Rehacom computerized software and Youth-Pediatric Symptom Checklist (Y-PSC) for evaluating their behavioral and emotional functions. Results: The results of the present study showed statistically significant differences between both groups regarding to (Y-PSC) score (p = 0.003). There was no significant difference in alertness with and without warning sound between both groups (p = 0.85, 0.89( respectively while there was a significant decrease in selective attention regarding reaction speed and reaction control of group B compared with that of group A (p = 0.04, 0.03) respectively. There was no significant difference in divided attention regarding auditory and visual modality between both groups (p = 0.42, 0.82) respectively. Regarding spatial number search, there was no significant difference in attention and neglect/ hemianopsia between both groups while there was a significant decrease in working speed of group B compared with that of group A (p = 0.36, 0.45, 0.01) respectively. No significant difference was found between both groups in working memory while there was significant decrease in memory for words of group B compared with that of group A (p = 0.79, 0.01). Significant decrease was found in logical reasoning of group B compared with that of group A (p = 0.03). There was a significant decrease in number of correct solutions of group B compared with that of group A (p = 0.03). Regarding visual field sub-domains (visual scanning and visual field deficits), no significant difference was found between both groups (p = 0.29, 0.11, 0.5). Conclusion: Prolonged smartphone usage was significantly associated with decreased cognitive functions. Specifically, the high risk smartphone users demonstrated a significant decrease in selective attention, working speed, memory for words, and logical reasoning.