The pollution standards index peaked at 371 on Thursday, breaking previous records and well above hazardous levels, before falling to about 300.
The haze is the result of forest fires started by farmers clearing land on the Indonesian island of Sumatra.
The issue has sparked accusations between the two neighbours.
Dr Vivian Balakrishnan, Singapore's Environment and Water Resources Minister, wrote on his Facebook wall that he would demand "definitive action" from Jakarta.