Robert Mertens's day gecko (Phelsuma robertmertensi) is diurnal species of lizard in the family Gekkonidae.

The specific name, robertmertensi, is in honour of German herpetologist Robert Mertens.

[2][3] One of the smallest of its genus, P. robertmertensi can reach a total length (including tail) of about 11 centimetres (4.3 in).

[3] P. robertmertensi is often found on banana trees and in abandoned vanilla orchid plantations.

In captivity, it can be fed crickets, wax moth larvae, fruit flies, mealworms and houseflies.