The aim of this study was to investigated the effects of erythromycin on cat myometrium in vitro. After myometrial samples was contracted with oxytocin 0.6, 1.2, 1.8, and 2.4 mM erythromycin was applied and effects on peak amplitude and frequency of contractions were investigated by 10 minute intervals. The frequency of oxytocin-induced contractions was 11.4±0.4 whereas 15.4±1.4, 28± 3.5 (P<0.001), 20±1.2 (P<0.001) and 4± 0.6 (P<0.001) after application of 0.6 mM, 1.2, 1.8 and 2.4 mM erythromycin, respectively. The mean peak amplitude of oxytocin-induced contractions was 3.37±0.41,after application of 0.6 mM, 1.2, 1.8 and 2.4 mM erythromycin dose-dependently decreased the the amplitude values to, 3.4±0.25 (P<0.001), 2.56±0.22 (P<0.001), 2.17±0.18 (P<0.001) and 0.65±0.15 (P<0.001), respectively. In conclusion, it was found that erythromycin in low doses inhibits amplitude of contractions but increase frequency, whereas high doses of erythromycin inhibits both amplitude and frequency of oxytocin-induced contractions of myometrium obtained from cat.