Carbonization of coffee husks (CHs) at different temperature, 350°C, 400°C, 450°C and 500°C followed by sulfonation with sulfuric acid gave solid carbon acid catalysts: CHs-350-SO₃H, CHs-400-SO₃H, CHs-450-SO₃H and CHs-500-SO₃H. The results of total acid density of the catalysts determined by titrimetry method range from 2.88 to 3.88 mmol/g and the –SO₃H density from 0.64 to 1.24 mmol/g. The catalysts were found by XRD to have a unique amorphous structure. FT-IR results show that the catalysts contain three functional Brönsted acid sites: weak acidic OH and COOH groups and strong acidic SO₃H groups. The solid acid catalyst prepared at 400°C (CHs-400-SO₃H) have exhibited the highest catalytic activity and good stability for the esterification of free fatty acids (FFA) in palm kernel oil with ethanol. This study provides an insightful knowledge on the resourceful transformation of a non-edible lignocellulosic solid waste precursor to a highly efficient, benign, and recyclable solid acid catalysts.