The present study aimed to investigate the efficacy of adenotonsillectomy (AT) for children with obstructive sleep apnea syndrome (OSAS) and the improvement of their cognitive function. Studies on cognitive performance of OSAS children treated with or without AT were identified by searching the Pubmed, EMBASE and Cochrane library. A meta-analysis was conducted to analyze the literature. The random-effects model was used to evaluate 11 eligible studies using an inverse- variance method. The neuropsychological test results of 4 cognitive domains (general intelligence, memory, attention-executive function and verbal ability) were obtained and analyzed. By comparison of cognitive function between OSAS children and healthy controls, the effect sizes of each domain were achieved as follows: general intelligence,-0.5 (P < 0.0001); memory,-0.18 (P=0.02); attention-executive function,-0.21 (P=0.002); and verbal ability,-0.48 (P=0.0006). The effect sizes of general intelligence, memory, attention-executive function, and verbal ability after AT compared to baseline level were-0.37 (P=0.008),-0.36 (P=0.0005),-0.02 (P=0.88), and-0.45 (P=0.009), respectively. Comparing the cognitive ability between OSAS children after AT and healthy controls showed that the effect sizes were-0.54 (P=0.0009),-0.24 (P=0.12),-0.17 (P=0.35), and-0.45 (P=0.009) in general intelligence, memory, attention-executive function, and verbal ability, respectively. Our results confirmed that OSAS children performed worse than healthy children in terms of the 4 cognitive domains investigated. After 6-12 months of observation, significant improvement in attention-executive function and verbal ability were found in OSAS children treated with AT compared to their baseline level; restoration of attention-executive function and memory were observed in OSAS children after AT in comparison to healthy controls. Further rigorous randomized controlled trials should be conducted to obtain definitive conclusions.