A trial to genotoxic evaluate for field-sampled microplastics by in vitro micronuclei test using CHL/IU cells was conducted. Primary microplastics (plastic pre-production resin pellet mixtures) and secondary microplastics (product-derived plastic fragment mixtures) collected in the coast of Ainoshima Island, Kitakyushu City, Fukuoka Prefecture, Japan in 2017 and 2018 were examined. The collected samples were extracted at 0.2g/mL using the culture medium with FBS. In short treatment with S9 mix and continuous treatment without S9 mix, the micronuclei tests of these medium extract of plastic pre-production resin pellet mixtures were negative. On the other hand, the results of product-derived plastic fragment mixtures showed positive. This is the first study evaluated the in vitro genotoxicity of field-sampled plastic marine debris using an international standard test method.