Cassia singueana (Del) is a shrub or small tree found in most part of northern Nigeria. Ethno medicinal survey reveals that the plant (root, leaf and stem bark) are being used in the treatment of malaria, syphilis, ulcer, pneumonia, snake bite and eye infection. Other uses include against mental disorder, swollen breast, fever, hernia, abdominal pain, convulsion etc. This paper seeks to examine phytochemicals, LD₅₀ and intestinal contraction of the methanol stem bark extract of Cassia singueana (Del.) and acetylcholine on experimental animals. The results of the phytochemical evaluation revealed the presence of terpenoids, cardiac glycosides, flavonoids, saponins, cardiac glycosides and tannins. The lethal dose of the extract was found to be 2150 mg/kg bd. wt. ip, thus indicating that the plant is relatively safe. The grade dose response of this study revealed that acetylcholine produced a dose-dependent increase in contraction with the least response value of 24.1 mm to a maximum response value of 57.2mm; while the extract revealed a contraction response of 20.8 mm at the lowest concentration and 10.0 mm at the highest concentration. The normal response was 30.4 mm at the lowest concentration and 10.0 mm at the highest concentration. This sequence could be due to the presence of a competitive antagonist in the crude extract thereby inhibiting the agonist response to a lower limit.