Abstract: Microplastics (MPs) pollution has become a global environmental problem.A few papers reported that MPs could have toxic effect on microalgae.Moreover, due to their strong binding ability, MPs may induce joint toxicity with other contaminants.As microalgae are the most primary producers in water system, the toxic effect is likely to influence the stability of food chains in water and further bring potential risks to human beings.The present paper reviewed the current research achievements and possible toxicity mechanisms, including physical damage, shielding effect, oxidative stress, adsorption and hetero-aggregation.In addition, future research directions were also proposed and discussed.