Microplastics (MPs) are recognised as one of the pollutants with a vast number of environmental impacts. There are no reports about the global distribution of fine MPs which were measured with a harmonized method. In our monitoring project, number concentrations, sizes and 17 polymer types of MPs greater than 20 ㎛ have been investigated in the global oceans by using volunteer ships since Mar. 2020. MPs were collected by 11 volunteer tanker ships with the cooperation of a Japanese shipping company, NYK Line in the four oceans in 2021. Approximately 1 ㎥ of sea water samples at the depth of 3 - 14m were obtained from the hydrant of 11 volunteer tanker ships at 100 sites in the four oceans. Particulate matters were collected by plankton nets (10 ㎛ mesh) on site. The number concentrations of summations of 17 polymers ranged from 22 to 4,660 pieces m-3 in the four ocean. Their geometric mean was 260 pieces m-3. The highest concentrations were observed at Kamchatka current, California current, Kuroshio current and North Pacific Ocean. Interestingly, their polymer compositions were different from each other. Mass concentrations were calculated from our size data of observed 17 polymers and their specific gravity values. The mass concentrations ranged from 2.1 to 645 ng/L and their geometric mean was 41.1ng/L in the four oceans. The highest mass concentrations were estimated at different sites from the highest number concentrations sites. Finally, ecological risk assessment in the four oceans was tried by comparing our mass and number concentration distributions to HC5 from previous studies. Distributions of number concentrations were remarkably lower than reported HC5 values. However, distributions of mass concentration were the same range. This gap was caused by difference of MPs size between observed in our research and used for toxicity studies.