Sundadanio rubellus is a species of freshwater ray-finned fish belonging to the family Sundadanionidae, the tiny danios.

[3] It is endemic to Kalimantan, Indonesian Borneo, and known from the southern Kapuas River delta.

It lives in peat swamp forests.

[1] Sundadanio rubellus reaches a maximum size of 1.9 cm (0.75 in) standard length.

[4]