Morphological differences among males, females, and juveniles of Gekko gecko, collected from Saraburi Province, were studied. It was found that there were significant differences among groups in various characters (p < 0.05). Eye length and tail width could separate males, females, and juveniles from each other, whereas internasal distance, interorbital distance, eye to ear length, ear length, axilla to groin length, hand length, and toe IV width could separate adults from juveniles. G. gecko exhibited sexual dimorphism in some characters such as body size, head width, and tail width. Discriminant Function Analysis was used and the result provided two equations for predicting sexes and ages of G. gecko. The study on the foraging ecology of G. gecko was conducted at the residential complex, Khao Khiao Open Zoo, Khao Khiao-Khao Chomphu Wildlife Sanctuary, Chon Buri Province during July 2001 to June 2002. It was found that temperature, humidity, and insect abundance could affect the number and activity of foraging G. gecko. Foraging time was between 5 pm to 9 am. The peak of emergence time was between 6 pm to 8 pm and the peak of retreating time was between 4 am to 7 am. Major food items of G. gecko were insects in the Order Lepidoptera, Orthroptera and Coleoptera. Prey sizes of males, females, and juveniles were not significantly different, indicating that the prey size did not depend on the body size and head size of the geckos. The foraging behavior of G. gecko; foraging period, time moving, foraging attempt, foraging success, prey size consumed, and foraging distance did not vary among groups of males, females, and juveniles. However, males’ foraging behaviors tended to be more variable than the others. In addition, the variations in foraging behavior among individuals were found. All foraging strategies of G. gecko observed in this study could be explained by the optimal foraging theory.