In order to evaluate the effect of water deficit stress on yield and physiological characteristics of some Iranian melon accessions, an experiment was carried out in a split plot based on randomized complete block design with three replicates in research filed of university of Zanjan during 2015. Treatments consisted arrangement of three irrigation levels (100, 70 and 40% ETc) and 7 Iranian melon accessions (Ghalam Ghash, Roshe, Zerke, Rish Baba, Ghobadloo, Garake and Kalyar). In this experiment, antioxidant enzyme activity, stomatal conductance, proline content, leaf relative water content, cell membrane stability index, hydrogen peroxide and malondialdehyde was measured. The results showed that water deficit stress reduced cell membrane stability index, leaf relative water content and stomatal conductance) and yield. The highest proline content in “Garake”, and maximum catalase and peroxidase enzymes activity was observed in “Zerke” and “Gobadloo” respectively under deficit irrigation 40% ETc. Hydrogen peroxide and malondialdehyde contents significantly increased under water deficit stress. According to the results, the highest (65.17%) and lowest (41.16 %) yield reduction was observed in “Zerke” and “Rish Baba” accessions respectively under irrigation 40% ETc compared to irrigation 100% ETc, thah were sensitive and tolerance accession to the water deficit stress, respectively.