Since the mass production of plastic in 1940, contamination of marine environment by plastics particularly micro plastics has been a growing problem. Micro plastics are little plastic particles, fibers and granules which have been defined in different sizes such as diameter less than 10, 5, 2 and 1 mm. The micro plastics that are made in microscopic size and are used in cleaner and cosmetic materials, are called primary micro plastics and secondary micro plastics are derived from larger particles. Micro plastics are directly transmitted to rivers and then sea via wastewater influent or leachates from refuse sites. Micro plastics are found throughout the water column and due to their small size, micro plastics are considered bioavailable for organisms. Their composition and relatively large surface area make them prone for adhering waterborne organic pollutants such as PAHs, PCBs and DDT. Micro plastics consumption by marine organisms have been shown by environmental and laboratory studies. Although adverse health effects via micro plastics are not obvious alone, but the transition of chemical materials from microplastics to organisms throughout the food-chain is a significant concern. In this article, micro plastics properties, micro plastics production resources, their entering effects on environment have been considered.