Background: Treatment adherence is essential to maintain treatment effectiveness and reduce complications among patients receiving hemodialysis. Patients are required to attend scheduled dialysis sessions, complete the prescribed dialysis duration, take medications as directed, and follow fluid and dietary restrictions. However, adherence may vary across different components of the treatment regimen. Aim: To assess treatment adherence and identify associated reasons and factors among patients receiving hemodialysis. Materials and Methods: We conducted a cross-sectional study a total of 260 patients who are receiving hemodialysis at the ‘Medvic’ Hemodialysis Centers located at the First Central Hospital and the Third Central Hospital. We assessed treatment adherence using the Mongolian version of the End-Stage Renal Disease Adherence Questionnaire (ESRD-AQ). We evaluated dialysis attendance and duration, medication use, fluid restriction, dietary adherence, and adherence barriers. Differences in ESRD-AQ total scores across demographic and clinical characteristics were analyzed using the independent-samples t-test and one-way analysis of variance (ANOVA). Results: The mean ESRD-AQ total score was 1093.37±99.04. Most participants did not miss (92.3%) or shorten (94.2%) dialysis sessions. In contrast, 57.7% always adhered to fluid restriction and 50.0% always followed dietary recommendations. Although most participants considered treatment recommendations very important, adherence to fluid and dietary restrictions remained comparatively lower. Common barriers included forgetting medication (61.7%), difficulty controlling fluid intake (88.7%), and difficulty avoiding restricted foods (82.5%). ESRD-AQ total scores differed significantly by sex, age group, and employment status (p<0.05). Conclusion Overall adherence to the hemodialysis treatment regimen was relatively good, with high compliance with attendance and full dialysis duration. However, adherence to fluid restriction and dietary recommendations remained poor. Furthermore, patients faced challenges such as difficulty monitoring fluid intake, inability to abstain from restricted foods, and forgetting to take medication. The total treatment adherence score differed significantly by gender, age group, and employment status.