Artificial light at night (ALAN) shows a new ecological factor affecting organism through multiple approach. The impact of ALAN on understory plants is not well understood. We evaluated the effect of ALAN on LMA (leaf mass per area) of understory plants based on a two-year field light experiment in tropical rubber plant forest in south China. We hypothesized that 1) ALAN would increase light supplement aboveground and directly increase LMA and 2) ALAN would attracting insects then changing soil nutrients underground and indirectly decrease LMA. We measured canopy openness, LMA, soil nutrients and individual distance away from ALAN for two species (shade tolerant species: Colocasia gigantea and shade intolerant species: Melastoma candidum). We found a negative relationship between LMA and the strength of ALAN for C. gigantea, which suggests the presence of indirect effects of ALAN, while M. candidum did not show any patterns. Our results suggests that the effect of ALAN might different for shade tolerant and shade intolerant species.