Even though the esterification of FFAs is fast on acid catalyst, the transesterification is very slow. Hence, it is desirable to design a simple protocol to synthesize water-tolerant and inexpensive solid acid catalyst with strong acid sites to give a reasonable transesterification rate comparable to that of base catalyst. Recently, we have developed a simple and sustainable methodology for the preparation of sulfonic acid functionalized polycyclic aromatic carbon catalyst with esterification activity from bioglycerol (biodiesel by-product), glycerol pitch (waste from fat splitting industry) and commercial glycerol by involving in situ partial carbonization and sulfonation in a single pot (Prabhavathi Devi et al., 2009, 2011, 2012). These carbon catalysts exhibited excellent catalytic properties by demonstrating their effectiveness for the esterification of palmitic acid to its methyl ester, and esterification of FFA present in non-edible oils to biodiesel. In continuation of our efforts towards exploring the applications of the glycerol-based carbon acid catalyst having 1.6 mmol/g acid density with surface area of 0.21 m2/g (Prabhavathi Devi et al., 2012), we herein report a simple and highly efficient single step method for the production of biodiesel from high-acid value karanja oil by simultaneous esterification and transesterification in quantitative yield at 160 _C in 4 h.