Microhabitat selection by reptiles can be affected by a complex interplay of abiotic and biotic factors. The Brown Treesnake (Boiga irregularis) is an efficient nocturnal predator that hunts in the tropical forest canopy and on the ground, using visual and chemical cues. To identify the factors influencing Brown Treesnake microhabitat use, we experimentally manipulated an abiotic factor, moonlight level, and a biotic factor, prey presence. We hypothesized that (1) moonlight would affect microhabitat use and (2) the presence of prey would alter microhabitat use in various moonlight levels. Trials were conducted in a large laboratory chamber with artificial trees in simulated new, half, and full moonlight. In each trial, the snake's location in canopy, subcanopy, or open ground was recorded at 60-sec intervals for 100 min. Treesnake microhabitat use was determined in three moonlight levels without prey present and in two moonlight levels with a mouse (adult Mas musculus) or a Mangrove Monitor (juvenile Varanus indicus) present. The treesnakes used open ground areas more as moonlight decreased, and they used the canopy more as moonlight increased. No significant differences existed within a moonlight level between trials with or without prey. Thus, moonlight appeared to supercede prey availability in affecting Brown Treesnake microhabitat use. Additionally, the effect of nocturnal illumination on Brown Treesnake habitat use may also have important conservation implications regarding trapping techniques and deterring the snakes from specific areas.