Chitosan acts as an elicitor in many plant species.It not only activates the immune system of plants, but also increases the crop yields.The objective of this study was to investigate the effects of chitosan on physiological and morphological responses of two field corn genotypes, tolerant and susceptible, under hypoxia.A pot experiment was conducted using a split plot in completely randomized design with two main plots (M) and three subplots (S).Main plots were two genotypes of field corn: NSX 062030 (tolerant) and 30B80 (Pioneer, susceptible), and subplots were three treatment conditions: normal irrigation without chitosan application (I-NC), chitosan application before hypoxia (C-H) and hypoxia without chitosan application (H-NC).Slight genotypic differences were observed for aerenchyma development under hypoxia.However, various treatment conditions influenced the activity of nitrate reductase (NR), leaf greenness, number of prop roots, and aerenchyma development.C-H had positive effects on number of prop roots and aerenchyma development and also tended to retain leaf greenness.The highest leaf NR activity was detected under H-NC and did not differ significantly from that under C-H.However, C-H tended to show positive effects on soluble sugar accumulation, but did not show any significant differences from the others.