: Little information is available on the role of Vitamin D as a micro-nutrient deficiency with masticatory muscle efficiency and its effect on the function of removable prosthesis. The aim of this study was to evaluate the role of vitamin D on masticatory muscle activity among completely edentulous patients and its effect on the retention of removable complete dentures (RCDs). : A non-randomized clinical control trial was conducted on completely edentulous patients (60.53 ± 7.01 years) in the Indian population between 2017 and 2019. Subjects were evaluated for temporomandibular disorders according to the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). Serum Vitamin D (S Vit D) levels, Ultrasonography (USG), and surface Electromyography (sEMG) readings of the masseter muscle were recorded at enrolment (Level 0), after 3 months of Vitamin D therapy (Level 3), and after consecutive 3 months of maintenance therapy, i.e., after 6 months from baseline (Level 6). The fabrication of new RCDs was done for all after the enrolment, and the retention of RCDs was assessed by asking a question regarding denture retention and asking respondents to mark their satisfaction on a 5-point Likert scale. Data were analysed using ANOVA, Paired'-test and Pearson correlation coefficients. A -value less than 0.05 indicated a statistically significant association. : Between enrolment and a six-month follow-up, S Vit D levels showed an increase from 16.03 ± 5.68 ng/mL to 31.35 ± 9.28 ng/mL, showing an increase of 15.32 ± 9.38 ng/mL (95.57% rise). Statistically significant values were observed for USG and sEMG. : Results showed that S Vit D affects masticatory muscle activity by improving its thickness and boosting its tonicity. Healthy muscles assist in the retention of RCDs, consequently aiding in mastication, speech, and phonetics, hence improving patient satisfaction. Clinical implication: Acknowledging the fact that the prevalence of Vitamin D deficiency is worldwide. We suggest Vitamin D therapy as a nutritional intervention among the elderly completely edentulous population, following dietary counselling, and consider Vitamin D therapy to be an adjunct to nutritional counselling for improving masticatory muscle activity and efficiency, which aids in RCD retention and stability. Consequently, improving oral health-related quality of life for individuals.