The present study was conducted to evaluate the effect of Poly-3-Hydroxy butyrate against the sporulation of oocyst of E. tenella. In this study four different doses of PHB which was extracted from the Bacillus subtilis culture, 10, 20, 50and 100mg were used with 2.5% potassium dichromate as positive control and distilled water as negative control. The experiment was carried out in 24 well plates. The sporulation efficiency was evaluated by counting the sporulated and unsporulated oocysts using haemocytometer and percentage efficiency of sporulation inhibition was calculated. Data were analysed using chi square test. The PHB at 100mg concentration showed significant effect on sporulation inhibition when compared to other doses of PHB and positive control.