The present study examines the responses of growth, oxidative stress and antioxidant enzymes in two Azolla species (Azolla pinnata and Azolla microphylla) exposed to pretilachlor, a herbicide commonly used in rice field and enhanced ultraviolet-B (UV-B) radiation. Both species of Azolla were exposed to different concentration of pretilachlor (5, 10 and 20 μg ml-1) and enhanced UV-B (UV-B1: ambient + 2.2 kJ m-2 day-1 and UV-B2: ambient + 4.4 kJ m-2 day-1) alone and in combination. The dry mass, superoxide radical formation, lipid peroxidation, enzymatic antioxidants i.e. superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (POD), and nonenzymatic antioxidant proline were investigated under pretilachlor and UV-B stress. Pretilachlor and UV-B stress caused negative impact on growth of both the species in dose dependent manner. The damaging effect was further enhanced by combination of both the stresses that was due to generation of superoxide radical and lipid peroxidation (MDA). Both the stresses alone and together also caused the increase in activity of SOD, CAT and POD, and proline accumulation. Compared to individual effect of pretilachlor and UV-B, the simultaneous exposure resulted in a strong inhibition of growth and excessive accumulation of ROS, thereby causing severe oxidative damage as evidenced by increased content of MDA, despite increased level of antioxidants. The overall results showed that pretilachlor and enhanced UV-B adversely affected growth in both species and their combined doses further deteriorated the growth. Results also showed that A. microphylla is comparatively less affected by pretilachlor and enhanced UV-B radiation than A. pinnata. The study also suggested that A. microphylla may used to grow for mass cultivation for medicine production and also as biofertilizer.