Surface tensions of aliphatic polyesters having different lengths of the methylene sequence were measured by the sessile bubble method from 120 to 160 degrees C. Surface tension decreased with an increase in the number (m) of carbon atoms in the methylene sequence. The linear relationship between gamma and l/(m+1) was derived from Sugden＇s equation which defined the parachor and the measured values fell on a single straight line. Surface tension of the eater group was also estimated as 56.6 dyn/cm.