A variety of exogenous physical factors such as width (or diameter), curvature and surface texture of the pupational substrate and relative humidity were found to exert significant influences on pupal color determination in Papilio protenor, though none of them was a major determinant. Green pupae tended to be formed in larger proportion when pupation occurred on narrower, curved or smoother substrates or at higher relative humidity.In conclusion, a pupal coloration is very likely to be determined by a reciprocal balance of intensity of environmental stimuli (physical and chemical) experienced by pupating larvae.