Abstract: The effects of ceftriaxone on isolated non-pregnant and pregnant rat uterus have been investigated. The isolated uterine horns were mounted into organ bath containing De Jalon’s solution connected to an oscillograph with an isotonic transducer to measure the contractions. Ceftriaxone was injected into the organ bath to study the pharmacological effects on the uterine smooth muscles. Trials were performed to locate the site of action of ceftriaxone on rat’s uterus and the obtained results revealed that ceftriaxone had a depressant effect on rats at various stages of sex cycle. It had a direct myometrial depressant effect since, presence of acetylcholine in a small concentration (0.25 μg mL-1 bath) produced its stimulatory effect in the presence of ceftriaxone 256 μg mL-1 bath and 256 μg mL-1 bath of ceftriaxone relaxed the uterus after its stimulation with propranolol 1 μg mL-1 bath.