In recent decades, the threat of microplastics to environment has become more and more serious. Microplastics will not only cause organ damage or death of aquatic organisms, but also accumulate into human body through food chain organisms after absorbed by aquatic organisms. Microplastics's invasion is not only through the food web, but also through daily necessities. The purpose of this study is to further analyze the distribution and abundance of microplastics and the proportion of microplastics of different sizes between two Swedish river systems. In this experiment, samples were taken from upstreams, lakes and downstreams of two different river systems. The particles of microplastics with two diameters (0.55-0.9mm and 0.9-2mm) and the proportion of microplastics with two different diameters were measured. Statistic analysis showed that there was no significant difference between the proportion of different size microplastics in different geographical locations or the particles of microplastics in two river systems. However, high concentration of microplastics were found in the lake and downstream location in the Nissan River. The proportion of microplastics with smaller diameter in the upstream locations was higher, which means that, although microplastics travelled downstream with the current, they accumulated in the lower reaches to a higher degree.