Background: Achieving precise surgical margins is crucial in tumor resection to minimize recurrence and preserve healthy tissue. Preoperative MRI-guided surgical planning has been proposed to enhance margin accuracy. This in vitro phantom study evaluates the impact of MRI-guided planning on surgical margin precision in tumor resections. Materials and Methods: A total of 30 phantom tumor models were created using synthetic materials mimicking soft tissue properties. The models were divided into two groups: MRI-guided surgical planning (n = 15) and conventional planning (n = 15). Preoperative imaging was conducted using a high-resolution 3T MRI scanner, and resection was performed using standardized surgical protocols. Margin precision was assessed by measuring the mean deviation from the intended margin using histopathological analysis. Statistical analysis was performed using a t-test, with a significance level set at p < 0.05. Results: The MRI-guided group demonstrated significantly improved margin precision, with a mean deviation of 0.8 ± 0.2 mm, compared to 2.3 ± 0.4 mm in the conventional group (p < 0.01). Additionally, the rate of positive margins was lower in the MRI-guided group (6.7% vs. 26.7%). The results indicate that MRI-guided surgical planning enhances resection accuracy and reduces margin variability. Conclusion: Preoperative MRI-guided surgical planning significantly improves margin precision in tumor resection. These findings suggest that incorporating MRI guidance into surgical workflows may enhance oncological outcomes by reducing positive margins and preserving adjacent healthy tissue. Further clinical studies are needed to validate these findings in patient populations.