The main aim of the study was to determine the least cost ration and optimum marketing weights for broiler chicken when groundnut meal is the main sources of protein in the broiler finisher ration. The data for the analysis was obtained from the National Animal Production Research Institute, Shikao The data was from experiments that covered aspect of broiler production with groundnut meal as the main protein source at protein levels of 17, 20, 23, 26 and 29 per cent finisher rations. Three production function equations were fitted to the data. They are Cobb-Douglas, Square root and the Quadratic functions. Computer facilities using the SPSS package was employed to estimate the parameters of the multiple regressions. However only the results of the Cobb-Douglas and the Quadratic equations were used for economic interpretations because they appropriately reflected the production process under study as shown by the statistical results. Total weight gain and marginal physical products of each of the rations were estimated from a global Cobb—Douglas production functions. The result indicated that rations high in protein provide greater gain per unit of feed at lower weights. For example l000g of 17 per cent ration produced weight gain of 382.4g and 23 per cent protein ration produced 424.l0g. But at higher feed intake and heavier weights, rations lower in protein content became more efficient. For instance at feed intake of 2200g 23 per cent protein ration produced weight gain of 808.21g while 29 per cent protein ration produced weight gain of 796„66g. Those conditions reflect the physiological requirements of the growing birds. At earlier stages of growth more protein is needed for body building but at later stages of growth more carbohydrate is needed for muscle development. The analysis also shows that the feed 20 per cent ration will give the least cost ration under a situation of profit maximization subject to feed cost constraint with prices of yellow maize and groundnut meal of 31 k/kg and 29 k/kg respectively. But if cost is to be minimised subject to output constraint then 23 per cent finisher ration will give the highest gross margins above feed costs as well as some other variable costs, with the stated input prices. It is still profitable to use groundnut meal even at a price increase of 42 per cent provided prices of other inputs are rot increasing.