Lactide production and racemization under microwave irradiation are compared with those under conventional heating. The amount of lactide including L,L-, D,D-, and meso-lactides that was produce in the reaction mixtures under microwave irradiation at 25 mmHg and 180 degrees C for 12 h was almost 2.7 times the corresponding amount produced under conventional heating. The ratio of the number of meso-lactide to the total number of lactides was higher under microwave irradiation than under conventional heating by a factor of 8.9. These differences between lactide production under microwave irradiation and that under conventional heating became increasingly noticeable as the reaction time and temperature increased. However, it was observed that at pressures under 15 mmHg, the ratio of the number of mesolactide to the total number of lactides under microwave irradiation was decreased and became equal to the corresponding value under conventional heating.