Abstract: Objective: To compare the efficacy and safety of low concentration of ropivacaine and bupivacaine used in improving bilateral superficial cervical plexus nerve block anesthesia. Methods: Eighty ASA Ⅰ or Ⅱ adult patients who underasent subtotal thyroidectomy were randomly divided into group R with 0.25% ropivacaine and group B with 0.25% bupivacaine(n=40,each). Two groups were treated with the method of improved bilateral superficial cervical plexus block,the local anesthetic drug directly injected in middle point of rear edge of sternocleidomastoid muscle by subcutaneous injection. The efficacy, muscle strength of neck and complications of cervical plexus block were assessed by anesthetist and surgeon. Heart rate(HR),and systolic blood pressure(SBP), diastolic blood pressure(DBP),pulse oxygen saturation(SpO₂) were monitored before block anesthesia(T₀),10 minutes after block anesthesia(T₁),incision of skin(T₂),and operation(T₃),and after operation(T₄). Results: There was significantly difference about the onsetime between group R(6.33 ±0.92) min and B(4.75 ±0.92) min(P < 0.01),without statistical difference about the efficacy of anesthesia between group R(95.0%) and B(97.5%), and complications(P > 0.05). Compared with T₀ point,HR significantly increased at T 2,T₃ point in B group (P < 0.05). DBP and SpO₂ both increased compared with T₀ at T₂, T₃, T₄ in two groups (P < 0.05-P < 0.01) without statistical difference of other indicators between two groups(P > 0.05). Moreover muscle strength of 4 cases case of muscle strength weakened can be found in group B. Conclusions: Ropivacaine is more suitable for improved bilateral superficial cervical plexus block anesthesia due to its efficacy and safety.