The aim of this experimental study was to assess whether 5 weeks of preoperative supplementation with vitamin D affects the intensity of pain and the level of inflammatory markers in patients undergoing posterior lumbar interbody fusion (PLIF) followed by rehabilitation. 42 patients were divided, by double-blind randomization, into two groups: supplemented (SUPL) vitamin D (3200 IU dose of vitamin D/day for 5 weeks) and placebo group (PL) treated with vegetable oil. The 10-week program of early rehabilitation (3 times a week) was initiated 4 weeks following PLIF. Measurements of serum 25(OH)D and CRP, IL-6, TNF-α, and IL-10 were performed. Pain intensity was measured using VAS. After supplementation with vitamin D serum, the concentration of 25(OH)D significantly increased in the SUPL group ( < 0.005) and was significantly higher as compared to the PL group ( < 0.001). A significant reduction in pain intensity was observed 4 weeks after surgery and after rehabilitation in both groups. In the SUPL group, serum CRP and IL-6 concentration significantly decreased after rehabilitation, compared with the postsurgical level ( < 0.04). The level of TNF-α was significantly lower after rehabilitation only in the supplemented group ( < 0.02). There were no significant changes in the IL-10 level in both groups during the study. Our data indicate that supplementation with vitamin D may reduce systemic inflammation and when combined with surgery and early postsurgical rehabilitation, it may decrease the intensity of pain in LBP patients undergoing PLIF. Data indicate that LBP patients undergoing spine surgery should use vitamin D perioperatively as a supplement.