Abstract Introduction Insomnia and obstructive sleep apnea(OSA) may co-exit, and it is now named comorbid insomnia and OSA(COMISA). Such combined condition is associated with increased morbidity, and impairment, which requires treatment for both insomnia and OSA. Bioelectrical impedance analysis(BIA) is a widely used convenient method of body composition. In OSA patients, muscle and fat distribution are different among different sex, and severity of OSA. We hypothesized that the muscle distributions in COMISA were different from OSA, which can help early identification COMISA to optimize treatment. Methods All the patients aged 18 or older with symptoms of sleep disturbances who visited single tertiary sleep clinic in Korea were enrolled from December 2017 to September 2022. All patients underwent structured sleep evaluation, insomnia severity index (ISI), overnight polysomnography and BIA. All patients with apnea-hypopnea index (AHI) 15 or greater were enrolled. The COMISA were classified by insomnia symptoms based on the ISI score greater than 15. Results Total of 3328 subjects were finally enrolled(79.7% males and 20.3% females), and among them 29.5%(n=981) was COMISA. Compare to OSA without insomnia symptoms COMISA were older(COMISA,56.6 ± 12.9, OSA,54.3 ± 13.3; p< 0.001), and were more likely to be female(COMISA,27.5%, OSA,17.3%; p< 0.001). Although AHI had no significance, apnea was lower, and hypopnea was higher in COMISA than OSA. The muscle distribution in COMISA was different compared to OSA in non-obese groups(BMI< 25). In both male and female, total muscle mass(MM), skeletal muscle mass(SMM), Rt and Lt arm(RAMM, LAMM), Rt and Lt leg(RLMM, LLMM), and trunk(TMM) muscle mass, and fat free mass(FFM) were significantly different between non-obese COMISA and OSA. The correlation analysis in non-obese COMISA group revealed that ISI is negative correlated with muscle masses in both sex (M:F); MM(M,F:rho:-0.09*,-0.16*), SMM(rho:-0.01*,-0.17*), RAMM(rho:-0.07*,-0.15*) LAMM(rho:-0.07*,-0.16*), RLMM(rho:-0.09*,-0,15*), LLMM(rho:-0.09*,-0.16*), TMM(rho:-0.08*,-0.17*), FFM (rho: -0.1*,-0.16*)[*p< 0.05]. Conclusion This study revealed that the muscle distribution is different in non-obese, male and female, moderate to severe COMISA population. And insomnia symptom severity has negative relation with trunk and limb muscle masses. Our study suggests possible insomnia symptoms among OSA patients have different pathomechanisms in relation to body muscle distribution. Support (if any)