Drosophila larvae innately show light-avoidance behavior. Compared with their robust blue-light avoidance, larvae exhibit relatively weaker responses to green light. We performed a screen for genes involved in Drosophila larval light-avoidance behavior. Compared with control w1118, larvae with γ-glutamyl transpeptidase 1 (Ggt-1) knockdown or Ggt-1 mutation were found to exhibit higher percentage of green-light avoidance which is mediated by Rh6 photoreceptors in Bolwig Organs. In contrast, their responses to blue light did not change significantly. By adjusting the expression level of Ggt-1 in different tissues, we found that functions of Ggt-1 in malpighian tubules were both necessary and sufficient for green-light avoidance. Our results showed that the level of GABA was lower in Ggt-1 mutants than in controls. Mutants in glutamate decarboxylase 1, which encodes GABA synthase, and knockdown lines of GABAA receptor, both demonstrated elevated levels of green-light avoidance.