The present work illustrates the synthesis of 4-sulfophenyl activated carbon based solid acid catalyst (ACPhSO<inf>3</inf>H), obtained from activated carbon (AC) by arylation with 4-sulfobenzenediazonium chloride. The variation of reaction conditions, such as, reaction temperature (20-85°C) and weight ratio of sulfanilic acid (precursor of 4-sulfobenzenediazonium chloride) to AC (0.14/1-14.00/1) provided ACPhSO<inf>3</inf>H with relatively high density of acid sites. The ACPhSO<inf>3</inf>H with the highest PhSO<inf>3</inf>H density (0.72mmol H<sup>+</sup>/g) was obtained using weight ratio of sulfanilic acid to AC (7.00/1) at 70°C after 10min. The catalyst was characterized by means of nitrogen adsorption analysis (average pore diameter 10.1nm, specific surface area 114m<sup>2</sup>/g, pore volume 0.29cm<sup>3</sup>/g), FT-IR, TG, XRD, FE-SEM and S elemental analysis. The spent catalyst can be easily regenerated recovering its initial density of acid sites. Upon employment in esterification reactions of rapeseed oil fatty acids, ACPhSO<inf>3</inf>H showed similar catalytic performance to Amberlyst-15.