The mountain kingfisher (Syma megarhyncha) is a species of bird in the subfamily Halcyoninae in the family Alcedinidae. Adult males are 21–24 cm long, and have a rufous head and underparts, greenish-blue upperparts, a dark blue tail, and black flight feathers. They also have dark neck patches and loral patches. Females have dark crowns and the neck patches join at the nape. It is similar to the yellow-billed kingfisher, but can be distinguished by its larger size and a proportionally larger bill, along with a dark ridge along its culmen.
It is endemic to New Guinea, where it is found through most of the New Guinea Highlands, except for the Bird's Head Peninsula. Its natural habitats are subtropical or tropical moist lowland forest and subtropical or tropical moist montane forest. It is found at elevations between 1,200–2,400 m, although it has also been reported as low as 700 m.
It feeds on small lizards, larvae, and insects. It lays eggs in December, and eggs are laid in clutches of two. The IUCN classifies it as a least-concern species.