Abstract: It is not clear whether the Silver nanoparticles (AgNPs) with different morphologies have different toxi-city to Scenedesmus Obliquus. In order to reveal the toxic effects of Scenedesmus Obliquus exposed to different morphologies of silver nanoparticles, Silver Nano Spheres (AgNSs) and Silver Nano Cubes (AgNCs) were exposed to the algae at 0, 5, 10, 15 and 20 mg/L respectively, observing the physiological and biochemical responses of the tested organisms. The results showed that the exposure of AgNSs and AgNCs both had significant toxic effects on Scenedesmus Obliquus, which showed damage of photosynthetic system and enzyme stress reaction: (1) Under 12-48 h exposure, mass concentration of Chlorophyll a in all treatment groups decreased significantly, but there were also obvious differences. When the AgNSs concentration reached 10 mg/L, the Chlorophyll a inhibitory effect could be significantly produced, and when the AgNSs concentration was greater than 10 mg/L, the inhibitory effect remained stable. While AgNCs significantly inhibited Chlorophyll a when the concentration was only 5 mg/L, and the inhibition effect was alleviated at 20 mg/L. (2) There are differences in typical enzyme stress responses between AgNSs and AgNCs exposure: The content of Reactive Oxygen Species (ROS) was significantly lower than that of the latter. The malondialdehyde (MDA) content of AgNSs was higher when the mass concentration of AgNSs and AgNCs were less than 15 mg/L, and the results were opposite when mass concentration of AgNSs and AgNCs were more than 15 mg/L. The superoxide dismutase (SOD) activity of the former remained stable while that of the latter decreased when the mass concentration of AgNSs and AgNCs were above 5 mg/L. (3) The difference of typical enzyme stress response between AgNSs and AgNCs was related to particle size, specific surface area and geometric shape. The results of this study can provide basic data for the emission control of silver nanoparticles in water environment.