A study on the prevalence of gastrointestinal helminths of Tilapia zilli was conducted from August to September, 2010 using standard parasitological techniques. A total of 150 Tilapia zilli were examined. The result shows that Caryophyllaeus species has highest prevalence of 16 (57.10%), while Cystacanthus and Diphylloborium species had 8 (28.60%) and 4 (14.30%) respectively. Based on sex male Tilapia zilli had higher 64.30%(18) prevalence of helminthiosis compared to that of females 35.70%(10)(p= 0,021< 0.05). T. zilli within the length categories of 16-20 and 21-25cm recorded a significantly (p= 0.012< 0.05) higher infection of 25.00%(7) and 60.70%(17) respectively. The lowest 14.30%(4) rate was observed in fish with 20 to 30cm categories. In conclusion, smaller Tilapia zilli were more susceptible to parasitic infections than larger ones.