Abstract: Thirty six weeks old (Large white X Landrace) hybrid weaner pigs (fifteen females and fifteen males) were used in a 12-week experiment to determine the cost effectiveness of substituting rubber seed cake for groundnut cake on the growth rate of weaner pigs. Graded levels of rubber seed cake (0%, 25%, 50%, 70% and 100%) replaced corresponding levels of groundnut cake in five Iso-Nitrogenous and Iso-caloric treatments (A, B, C, D and E) respectively which were further replicated three times in a completely randomized design. Feed and water were supplied ad libitum to the experimental pigs while medication (wormers) were administered to maintain good health. Feed intake was recorded everyday while body weight was taken every week in all the treatments. The average weight of pigs at eighteen (18) weeks were 40.30c, 41.70bc, 39.30c, 41.80b and 47.20a for treatments A, B, C, D, E respectively while the average feed cost (naira) per kilogram of pork gained were N86.95a, N77.47b, N84.04a, N68.00bc and N56.56c for treatments A, B, C, D, and E respectively. Results showed that treatment E had both significantly (P< 0.05) higher weight gain and lowest cost of production.