Sixty elderly patients undergoing unilateral total hip arthroplasty (THA) were randomized to receive erector spinae plane block (ESPB) with either ropivacaine & dexamethasone or ropivacaine & saline. All blocks were performed at L3 under ultrasound guidance, immediately after spinal anesthesia. The primary outcome was time to first rescue opioid. Secondary outcomes included 48-hour opioid consumption, numerical rating scale (NRS) pain scores, quadriceps strength, nerve injury scores, and blood glucose levels. Outcomes were measured at 4, 8, 12, 24, and 48 hours postoperatively. Overall, the results of the study revealed that perineural dexamethasone produced markedly longer analgesia and significantly reduced postoperative opioid needs, with consistently lower pain scores beyond 8 hours. Motor strength, nerve integrity, and blood glucose remained unchanged between groups. These findings demonstrate that dexamethasone is a safe and highly effective adjuvant for prolonging ESPB analgesia in THA.