Background: The number of bariatric surgeries has increased in recent years, and major attempts have been made to find the best surgical procedure. Laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB) are the most common bariatric surgery procedures. This study aimed to investigate the effects of these two procedures on improving sleep quality, daytime sleepiness, and obstructive sleep apnea. Materials and Methods: This case-control study was performed on two groups of patients (n=60 per group). The case group included obese candidates for LSG or RYGB, and the control group consisted of obese patients without any surgical interventions. The sleep quality, obstructive sleep apnea (OSA) risk, and daytime sleepiness were examined, using the Pittsburgh Sleep Quality Index (PSQI), Stop-Bang questionnaire, and Epworth Sleepiness Scale (ESS), respectively. The results were recorded before and six months after the intervention and compared between the two groups. Results: There was no significant difference in the mean scores of ESS, PSQI, and Stop-Bang questionnaire between the two groups before the intervention (P>0.05). However, the mean scores of PSQI and its dimensions, ESS, and Stop-Bang questionnaire significantly improved in patients undergoing surgery (p <0.05). The results of linear regression analysis also showed significant improvements in the ESS, PQSI and Stop-Bang scores in the intervention group. Body mass index (BMI) reduction improved the scores of PSQI, ESS, and Stop- Bang questionnaire in patients, with impact factors of 0.032, 0.700, and 0.025, respectively (p <0.05). Conclusion: LSG and RYGB surgeries significantly improved the patients’ sleep quality, decreased daytime sleepiness, and reduced the risk of OSA. Overall, BMI reduction and lack of OSA can significantly affect sleep quality.