The present work demonstrates a single-step preparation of sulfo carbon-based solid acid catalyst (CSO3H) obtained from cellulose by direct carbonization-sulfonation with conc. H2SO4. The variation of reaction conditions, such as, reaction temperature (50-180 degrees C), weight ratio of H2SO4 to cellulose (5/1-30/1) and reaction time (1-10h) provided CSO3H with relatively abundant density of acid sites attached on catalyst surface. The CSO3H with the highest density of SO3H groups (0.81 mmol H+/g) was obtained at 100 degrees C using weight ratio of H2SO4 to cellulose (20/1) after 3 h of reaction. The catalyst was characterized by means of N-2 sorption analysis (average pore diameter 12.8 nm, specific surface area 1.38 m(2)/g, pore volume 0.004 cm(3)/g), FT-IR, TG, XRD, FE-SEM and S elemental analysis. The conversion of rapeseed oil fatty acids (RFA) in esterification reactions with CSO3H as catalyst was quite similar to the commercial Amberlyst-15 and the biodiesel with ester content of >= 96.5% was successfully obtained under optimized reaction conditions. (C) 2016 Elsevier B.V. All rights reserved.