In this study, the effect of 5-Aminolevolinic acid (ALA), a key precursor in the biosynthesis of porphyrin and the new plant growth regulator, was studied on some physiological responses of coriander plant under drought stress. The layout was a factorial experiment in randomized complete block design (RCBD) with three levels of drought stress (irrigation within 100%, 60% and 30% field capacity) and four concentrations of ALA (0, 0.25, 0.5 and 1mM) as factors. The experiment was conducted in the greenhouse of agricultural faculty of Ilam University in 2010. Statistical analysis showed the significant effects of the drought and ALA on plant physiological parameters including leaf relative water content (RWC), water use efficiency (WUE), praline, malondialdehyde (MDA) and chlorophyll content. In drought conditions, chlorophyll content and RWC were reduced but MDA accumulation, praline content and WUE increased. ALA application significantly caused increasing of RWC, WUE, chlorophyll content and proline accumulation and decreasing of MDA content in plant. In this study, ALA treatment with increasing of praline and chlorophyll content and reducing of MDA accumulation decreased the adverse effects of drought stress on the coriander plant.