【】 Objective To determine the 95% effective dosage of 0.15% ropivacaine used for ultrasound guided stellate ganglion block(SGB)at C7 level.Methods TenSinsomnia patients aged 20-60 years old including male 5 and female 5 with ASA I-II were scheduled to receive 2 times SGB with 0.15% ropivacain at 1 day interval.Using the transverse short-axis view with out-of-plane of the neck at the C7 level,the liquid medicine was injected via the lateral paracarotid approach targeting between the prevertebral fascia and the ventral surface of longus colli muscle(subfascial injection).The volume of 0.15% ropivacaine injected in each patient was based on cross-sectional effective dosage of 0.15% ropivacaine for ultrasound guided SGB.The initial volume was 4 ml and each time the volume was increased by 0.4 ml if the block failed while the volume of ropivacaine was reduced by 0.4 ml if block succeeded.A successful block was confirmed with the onset of ptosis(Horner’s syndrome).The ED₉₅ and 95% infidence interval of 0.15% ropivacaine were calculated.Result ED₉₅ of 0.15%ropivacaine for ultrasound guided SGB at C7 level was 0.16 ml,95% confidence interval was 1.17～2.03ml.Conclusion ED₉₅ of 0.15% ropivacaine for ultrasound guided SGB was 1.6 ml.