Purpose This study aimed to examine the synergistic effect of Vitamin D (VD) supplement and mindfulness on insulin resistance and different aspects of cognitive function in VD deficient type 2 diabetic women. Methods In this randomized-controlled trial, totally 225 women with type 2 diabetes mellitus (T2DM) and VD deficiency were randomly allocated to five groups: (1) mindfulness, (2) mindfulness and VD, (3) mindfulness and placebo, (4) VD, and (5) placebo. Mindfulness includes 12 sessions and VD patients received a daily 4000 IU oral dosage (two capsules) with 28,000 IU vitamin D weekly for 12 weeks. Sun exposure, anthropometric indices, dietary intake, physical activity, energy levels, and laboratory analyses were measured at the pre-test and after 12-week supplementation. Dependent variables include cognitive function (Risky decision making, IQ and Trail Making Test) and insulin resistance. Results In baseline, measures were not different among the groups. At the end of the treatment, cognitive function results showed improvement for all groups except the “placebo” group. About other groups, there was not any differences between VD and mindfulness groups (or combinations with placebo). However, in “VITAMIN + MINDFULNESS” group, a greater improvement compared to other groups was observed (P < 0.05). This result exactly repeated for insulin resistance. Furthermore, there were not any significant difference among groups for IQ (as one aspect of cognitive function) (P > 0.05). Moreover, there was not any differences among groups for sunlight exposure and BMI (P > 0.05). Only in combined group (VD + Mindfulness) the fasting blood sugar (FBS) significantly reduced that shows the synergistic effect of VD supplementation and Mindfulness (P < 0.05). Conclusion Combining VD Supplementation and mindfulness can reduce insulin resistance and improve different aspects of cognitive function in VD Deficient patients.