Hyperolius minutissimus is a species of frog in the family Hyperoliidae. Its common names are tiny reed frog and dwarf reed frog. It is endemic to Tanzania and known from the Udzungwa Mountains and from near Njombe in the Southern Highlands.
Males measure 12–17 mm (0.47–0.67 in) and females 18–24 mm (0.71–0.94 in) in snout–vent length; Loader and colleagues report larger male sizes (19–23 mm) from the Udzungwa Mountains, but no data on females.
The dorsum is brown and has light canthal and dorsolateral lines. Some females, however, have broad light canthal and irregular dorsolateral stripes, as well as spots on the dorsum. The pupil is horizontal. Males have a gular flap and black dotted asperities distributed on anterior and mid-region of the gular flap.