Thyroid surgery may cause severe postoperative pain and discomfort for patients. Superficial cervical plexus block (SCPB) is one of the regional anesthesia techniques that can provide postoperative analgesia for thyroid surgery. The purpose of this study was to evaluate analgesic effect of ultrasound (US) guided SCPB in patients undergoing thyroid surgery. Fifty ASA I-II patients, aged 20-60, were included in this single blinded study. In a randomized and prospective manner patients were allocated to either SCPB or control group. Bilateral SCPB was performed preoperatively under US guidance using 10 ml 0.25 % bupivacaine for each side. Postoperative analgesia was provided with patient-controlled analgesia method with morphine intravenous. Primary outcome measure was postoperative opioid consumption and analyzed using Mann-Whitney U test. Secondary outcome measures were comparison of opioid side effects like nausea and vomiting and analyzed using Chi square test. VAS scores for pain at postoperative 1st, 6th, 12th, and 24th h were similar in SCPB and control groups (Median VAS values were 2.5, 3, 2, 0 and 3.5, 3, 2, 0 respectively). Postoperative morphine consumption was lower in SCPB group compared to control group at postoperative 6th, 12th, and 24th h (Median doses of morphine consumption were 4, 8, 9 and 5, 9, 11 mg respectively) (P < 0.05). Eight patients in the control group and six patients in the SCBP group had vomiting. Seven patients in the SCPB and none in the control group had hoarseness. Our study has shown that US guided SCPB has a significant analgesic effect in patients undergoing thyroid surgery. Further studies are required to search for the optimal LA dose during US guided SCPB.