Due to its economic profitability and wide application, plastic has become an indispensable material in everyday human life. Plastic is broken down in environment by various physical and chemical processes into smaller plastic particles, which is then known as microplastics (MP). Degraded MP particles later become a big problem and a threat to the ecosystem and organisms that come into contact with it, because they more easily interact with organic and inorganic pollutants and adsorb them. MP usually adsorbs heavy metals and gradually releases them into the environment. In this work the influence of pristine MP (a mixture of polyethylene, polystyrene, polypropylene and rubber particles) and MP contaminated with a mixture of heavy metals (copper, lead and zinc) was studied on the growth rate of greater duckweed (Spirodela polyrhiza L.) and on certain physiological and biochemical indicators of oxidative stress (photosynthetic pigments, carbonyls and malondialdehyde and activity of antioxidant enzymes). Release of metals from the MP surface into the nutrient medium was determined, as well as metal accumulation in the greater duckweed, though only accumulation of Cu at the highest concentration of MP contaminated with metals was statistically significant compared to control and other treatments. The growth rate was not statistically significantly affected by the seven-day exposure of duckweed to pristine MP and MP contaminated with metals. An increase in the activity of antioxidant enzymes was observed at the lower concentrations of pristine MP and at the higher concentrations of MP with adsorbed metals. Lipid peroxidaiton increased in response to MP contaminated with metals, while the content of carbonyls and soluble proteins did not change significantly. In conclusion, greater duckweed represents a suitable model for phytoremediation.