Objective: To study the effect of levobupivacaine and bupivacaine on the contractility of isolated uterine muscle strips from pregnant and non-pregnant female rats. Methods: Full-thick myometrial strips were prepared from 18- to 21-day pregnant (n=8) and non-pregnant rats (n=7). After contractions became regular, strips were exposed to cumulative concentrations of the two drugs from 10?8 to 10?4 mol/L, amplitude and frequency of the uterine contraction was recorded. Results: Two local anesthetics caused a concentration dependent inhibition on contractility of myometrial strips from pregnant and non-pregnant rats. In the myometrium from non-pregnant rats, ?logIC50 of levobupivacaine and bupivacaine were 4.85 and 4.25 respectively. In the myo- metrium from pregnant rats, similar concentrations of levobupivacaine and bupivacaine were observed, ?logIC50 were 2.7 and 2.9 respectively. Levobupivacaine produced an increase in amplitude of contractions, while bupivacaine showed an increased trend in frequency. Conclusion: These results demonstrate that levobupivacaine and bupivacaine may inhibit myometrium contractility. The inhibitory effect of levobupivacaine or bupivacaine is not enhanced by gestation in rat. Levobupivacaine may have more positive influence than bupivacaine in pregnant myometrium. Objective: To study the effect of levobupivacaine and bupivacaine on the contractility of isolated uterine muscle strips from pregnant and non-pregnant female rats. Methods: Full-thick myometrial strips were prepared from 18- to 21-day pregnant (n = 8) and Non-pregnant rats (n = 7). After contractions became regular, strips were exposed to cumulative concentrations of the two drugs from 10? 8 to 10? 4 mol / L, amplitude and frequency of the uterine contraction was recorded. local anesthetics caused a concentration dependent inhibition on contractility of myometrial strips from pregnant and non-pregnant rats. In the myometrium from non-pregnant rats, • log IC50 of levobupivacaine and bupivacaine were 4.85 and 4.25 respectively. In the myo- metrium from pregnant rats, similar concentrations of levobupivacaine and bupivacaine were observed, • log IC50 were 2.7 and 2.9 respectively. Levobupivacaine produced an increase in amplitude of contractions, while bupivacaine showed an increased tr Conclusion: These results demonstrate that levobupivacaine and bupivacaine may inhibit myometrium contractility. The inhibitory effect of levobupivacaine or bupivacaine is not enhanced by gestation in rat. Levobupivacaine may have more positive influence than bupivacaine in pregnant myometrium.