Mg-Al hydrotalcites with different Mg/Al molar ratios were prepared and characterized by XRD, FT-IR, SEM and BET analyses. The calcined hydrotalcite with Mg/Al molar ratio of 4.0 (LDO Mg/Al 4.0) exhibited the highest catalytic activity in the synthesis of propylene glycol methyl ether (PM). The catalytic activity relating to the amount of the basic sites and crystallinity depended on the Mg/Al molar ratio. The optimal equilibrium of acid-base property and high crystallinity made the LDO Mg/Al 4.0 an excellent catalyst in the reaction. Etherification of propylene oxide (PO) with methanol over the LDO Mg/Al 4.0 was researched. The optimized reaction conditions were as follows: 140 degrees C, catalyst amount 0.9 wt%, methanol/PO molar ratio 4.0 and 6 h. The PO conversion and PM selectivity were 93.2 and 97.4%, respectively. Above all, almost all the PM was 1-methoxy-2-propanol, for no 2-methoxy-1-propanol was detected by GC analysis in the reaction products, and the catalyst could be reused for five times.