Abstract This paper explored how heat treatment affects moisture sorption in amorphous, semi-crystalline and end-capped polylactides. End-group modified polylactide was synthesized by ring-opening polymerization with palmityl alcohol as the initiator and acetic anhydride as the terminating agent. Water sorption in amorphous standard polylactide is insensitive to heat treatment conditions but decreases with increasing molecular weight. Water sorption increases with increasing heat treatment temperature in low molecular weight, semi-crystalline standard polylactide but there is a negligible change with heat treatment conditions in high molecular weight semi-crystalline standard polylactide. Water sorption in standard polylactide is strongly affected by the content of hydrophilic end in amorphous polylactide. In modified semi-crystalline polylactide, water sorption increased with increasing heat treatment temperatures or crystallinity. Water sorption in end-capped polylactide is influenced by morphology including crystallinity, microphase separation and amorphous phase composition produced by heat treatment conditions.