Abstract-Synthetic studies on methylation of erythromycin derivatives were conducted. Methylation of 6 resulted in the formation of the C-3/quatemary ammonium salts with a rate faster than 6-O-methylation. In dipolar aprotic solvent and under strong base conditions. 6-0-methylation, C-3r quaternary ammomum salts formation and 2-C-methylation proceeded simultaneously to yield a mixture of three different products 7, 8 and 9. The quaternary ammonium salts were converted back to the corresponding tertiary amines 2, 10 and starting material 6 by employing sodium 4-pyridinethiolate as a N-demethylation reagent. The 6-O-methylation was eventually achieved in a good yield when a carbobenzyloxy (Cbz) group was utilized to protect the C-3/-dimethylamino group of 4. In this report, we will discuss the details of different reaction courses in the methylation of (9S)-12. 21-anhydro-9-dihydroerythromycin A derivatives.