In general, microplastics (MPs) have been identified at higher concentrations in marine sediments than in seawater. This is attributed to the trapping effect of sediments on MPs. MPs in the ocean undergo a sinking process, ultimately accumulating in marine sediments. MPs have been identified as a significant threat to marine biodiversity, particularly in coral reef habitats, due to their potential carcinogenic effects. This study examines the correlation between MPs characteristics—specifically, size and shape—and sediment grain size with MPs abundance in adjacent coral reef sediments in Rembang Regency, Central Java, Indonesia. To achieve this, Pearson's correlation and principal component analysis (PCA) methods were employed. The findings indicate that most MPs are concentrated in nearshore regions near anthropogenic sources. Moreover, the correlation based on Pearsons was found to be particularly significant for MPs size, MPs shape, and grain size, with values of 0.84, 0.754, and 0.431, respectively. The PCA result demonstrates that the greater the abundance of MPs in the sediment, particularly those that are MPs smaller in size and compact shape, such as fragments and pellets, the greater the likelihood of their sinking and infiltration into the sediment. This finding highlights the crucial role of MPs size and shape in tight relationship to their density in determining the rate of sinking and infiltration of MPs into the sediment.