Andohahela Réserve Naturelle Intégrale is located in southeastern Madagascar. It consists of three parcels, the largest of which (Parcel 1, 63,100 ha), lying on the eastern flank of the Anosyenne Mountains between 90 and 1972 m elevation, is dominated by rain forest. We surveyed the herpetofauna of Parcel 1 at the beginning of the warm, rainy season between 20 October and 5 December 1995. We recorded 45 amphibian and 32 reptile species in Parcel 1, including a new species of Phelsuma, which we describe in this paper. This new species, Phelsuma malamakibo, is a medium-sized, rock-dwelling species which occurs in primary rain forest at elevations between 810 m and 1940 m. It is identified by the presence of a distinct dark lateral stripe on the neck and body with a white lateral stripe beneath it and a second, thin dark lateral stripe below the white stripe; greenish dorsal ground color with reddish brown spots arranged into three longitudinal rows or lines on the neck and back; no sexual dichromatism; a median cleft dorsally on the rostral scale; nostrils centered above the first supralabial scale; subequal subcaudal scales; keeled gular and anterior chest scales; and smooth (unkeeled) scales on the ventral surfaces of the body and tail. In most respects, this new species is similar to Phelsuma lineata, P. pusilla, and P. quadriocellata; however, these species have keeled ventral scales. Phelsuma malamakibo is similar to P. modesta in having smooth ventral scales, but the latter species is sexually dichromatic and differs from P. malamakibo in details of coloration and nostril position, as well as habitat. Phelsuma modesta is largely arboricolous in variable, usually drier habitats, whereas P. malamakibo is saxicolous in rain forest.