<p>While microplastics from lake, beach and ocean environment has become a growing global concern, tidal variations of microplastics in beach sediments are not well documented. Here, sediments were sampled over one monthly lunar tidal cycle during low tidal period in Shajing Beach along the Maowei Bay, China. The shape and abundance of microplastics were measured in sediments to determine their periodic variations by wavelet analysis method. The results showed that microplastics are generally granule, fiber and film shapes on Shajing Beach. The dominant type was fiber, followed by the granule. Meanwhile, the microplastic abundances showed a periodic change about 15 days. The granule and fiber but not film also followed such periodic variations. Tourism and human activities along the bay are the most likely causes for microplastics in Shajing Beach, while half-mouth of tidal cycle is responsible for the periodic variation of microplastic abundances and types.</p>