Background: The aim of this study is to evaluate the per se effect of cinnamaldehyde which is obtained from bark oil of cinnamon tree and its interaction with ondansetron on catalepsy in Swiss albino mice. Methods: Haloperidol induced catalepsy model was used. A group of 36 healthy mice of either sex weighing 20-30 grams were divided at random into six groups (n=6). Cinnamaldehyde with 98 percent purity was obtained. Catalepsy was induced by haloperidol (1mg/kg, i.p). Control group received tween-20 20% (10ml/kg, p.o), standard groups were administered ondansetron (0.5mg/kg and 1mg/kg, p.o ), test groups received cinnamaldehyde in strength of 100mg/kg, and 200mg/kg and combination group of ondansetron plus cinnamaldehyde (0.5mg/kg + 100mg/kg) per oral, respectively. Results: In this acute study, from 60 min onwards after haloperidol administration, ondansetron at both doses (0.5 mg/kg and 1 mg/kg), showed significantly lower cataleptic scores as compared to all groups. Cinnamaldehyde at both strengths did not show any significant effect as compare to control at any point of time (P>0.05). Combination of ondansetron 0.5 mg/kg with cinnamaldehyde 100mg/kg, showed significant increase in cataleptic score as compared to ondansetron 0.5 and 1mg/kg alone (P>0.05). Which suggest that cinnamaldehyde abolishes the protective effect of ondansetron in haloperidol induced catalepsy.