This study aimed to evaluate the effectiveness of Motivational Interviewing (MI) in reducing social desirability bias and vulnerability to stress among adults. A randomized controlled trial was conducted with 40 participants randomly assigned to either an intervention group (20 participants) or a control group (20 participants). The intervention group received ten 60-minute sessions of MI, while the control group received no intervention. Assessments for social desirability and vulnerability to stress were conducted at baseline, immediately post-intervention, and at a four-month follow-up. Data were analyzed using analysis of variance (ANOVA) with repeated measurements and Bonferroni post-hoc tests. At baseline, the intervention group had mean scores of 24.35 (SD = 3.12) for social desirability and 30.45 (SD = 5.27) for vulnerability to stress. Post-intervention, these scores significantly decreased to 18.75 (SD = 2.89) for social desirability and 21.30 (SD = 4.82) for vulnerability to stress. At the four-month follow-up, the intervention group maintained reduced scores of 19.10 (SD = 3.05) for social desirability and 22.05 (SD = 4.75) for vulnerability to stress. ANOVA results indicated significant between-subjects effects for social desirability (F(1, 38) = 92.45, p < .001) and vulnerability to stress (F(1, 38) = 105.92, p < .001). Bonferroni post-hoc tests confirmed significant reductions between baseline and post-intervention for both social desirability (mean difference = 5.60, p < .001) and vulnerability to stress (mean difference = 9.15, p < .001). Motivational Interviewing significantly reduces social desirability bias and vulnerability to stress among adults, with effects sustained over a four-month period. These findings support the use of MI in enhancing self-report accuracy and stress resilience in various therapeutic settings.