The ranat thum (Thai: ระนาดทุ้ม, pronounced [ranâːt tʰúm]) is a low pitched xylophone used in the music of Thailand.

It has 18 wooden keys, which are stretched over a boat-shaped trough resonator.

Its shape looks like a ranat ek, but it is lower and wider.

ranat thum bars are typically made from bamboo, although instruments with rosewood (Dalbergia oliveri; Thai: ไม้ชิงชัน; mai ching chan) bars can also be found.

It is similar to a Cambodian xylophone called roneat thung.