We report a new microhylid frog of the genus Kalophrynus from Peninsular Malaysia and describe it as a new species Kalophrynus kiewi based on results of molecular and morphological analyses. The new species is a large-sized Kalophrynus (snout-vent length 34–47 mm) and is morphologically very similar to K. pleurostigma, in which it has long been unrecognized, and K. meizon, but is distinguished from them molecularly and by its body size, dorsal skin texture, and relative length of hindlimb. The new species is also clearly differentiated from all the other members of the genus by molecular and morphological differences. Taxonomic and distributional problems of the genus Kalophrynus in Peninsular Malaysia are briefly discussed.