Leptolaena arenaria is a tree in the family Sarcolaenaceae. It is endemic to Madagascar.
Leptolaena arenaria grows up to tall with a trunk diameter of up to . Its bright green leaves are ovate in shape and measure up to long. The tree's flowers typically occur in inflorescences of two flowers, each with white petals. The roundish fruits measure up to in diameter. The species is used in local medicine.
Leptolaena arenaria is known only from the northwestern regions of Diana, Betsiboka, Boeny, Melaky and Sofia. Its habitat is in dry forests from sea level to elevation.
Leptolaena arenaria has been assessed as near threatened on the IUCN Red List. Its habitat is threatened by wildfires, conversion of land for agriculture and harvesting for wood. The species is present in some protected areas including Ankarafantsika National Park.