In this research, the zeolite-sulfonated carbon from sugar cane catalyst has been employed for the free fatty acid (FFA) esterification in sludge palm oil (SPO) optimised by response surface methodology and central composite design. The effect of the catalyst weight ratio of zeolite to sulfonated carbon was evaluated. The result showed that the catalyst with a weight ratio of zeolite to sulfonated carbon of 1:3 (% w/w) had the highest acidic value of 10.80 mmol g–1 and was used for further esterification optimisation. FTIR and EDX analysis affirmed the existence of a sulfonated group of the composite catalysts. The ¹³C NMR analysis showed that the esterification successfully produced an ester compound. The optimum conditions for FFA conversion were acquired at a reaction temperature of 78.98°C, a reaction time of 119.97 min, a catalyst weight of 2.97 g, with 94.19% FFA conversion, and followed by a statistically significant model. The catalyst reusability study revealed that the catalyst had a slight decrease in catalyst performance and could generate up to 80.00% conversion after the fourth cycle. This study could bring forth early information about the potential of zeolite-sulfonated carbon from sugar cane catalyst for FFA conversion from SPO into high-value ester products.