Abstract: Microplastics in marine environment mainly terrigenous plastic debris or those from marine vessel dumping and discarded floating devices in aquaculture,etc. Microplastics are easily taken unexpectively by marine organisms due to the food similarity of their size, shape and color. Microplastics have direct and potential effects to marine organisms and ecosystems due to the toxicities of microplastics and toxic chemicals adsorbed on their surfaces or released from microplastics. This paper reviews research progress in the effect pathways, toxic effects and mechanisms of microplastics on marine organisms. Furthermore, we propose that the following studies on microplastics in future should be focused on the longterm toxic effects under environmental concentrations, the effects and mechanisms of microplastic alone and its mixture with other pollutants，the biomarker selection and the ecological risk assessment.