Biodiesel production from the waste oils and fats are the cost effective methods and prevents the environmental pollution by proper disposal techniques. Converting waste oils/fat into biodiesel using alkaline catalyst is difficult, as it contains more than one percent Free Fatty Acid (FFA) which will form soap during the transesterification process. Hence, it is desirable to reduce the level of FFA lower than one percent for biodiesel production using the pre-treatment process. In the present research work, ferric sulfate (solid catalyst) is used as a catalyst, because it converts FFA efficiently than the homogeneous acid catalyst which is corrosive in nature and takes longer reaction time. The parameters used in the pre-treatment process are, amount of catalyst varying from 0.5 to 2% by weight, amount of methanol in moles ranging 3 to 15 to one mole of waste chicken fat (molar ratio), temperature ranges from 45°C to 65°C and the reaction time of 30 min to 150 min to find the effective conversion of FFA. The Response Surface Methodology (RSM), a statistical tool with the fitted quadratic polynomial equation which is obtained from the regression analysis is used to generate surface plots and optimize the pre-treatment process. Experiments are carried out to validate the equation using combinations of the independent variables. The confidence level of the empirical model of FFA conversion is 95%. It is observed that the molar ratio, amount of catalyst and time having more significant effect on the FFA conversion than the effect of temperature. The optimum conditions are found as catalyst amount 1.42% by weight, methanol to oil molar ratio of 10.89:1, temperature of 50°C and the reaction time of 117 min using the response surface methodology with 95% FFA conversion. Based on the optimum pre-treatment parameters, transesterification is done with alkaline catalyst (KOH) to produce the methyl esters of waste chicken fat. The properties of the waste chicken fat biodiesel are within the ASTM D6751 and EN14214 standards; hence suitable for the normal operation of a CI engine.