Hydroxymethylation of 6,8-O-dimethyl emodin was easily achieved in good yields by the modified Marschalk reaction. The influence of the amount of solvent, base and formaldehyde toward the hydroxymethylation was discussed. The results showed that a relatively dilute reaction solution facilitated the generation of the desired 2-hydromethyl product, while the thick reaction solution benefited the generation of the methylated quinizarins.