Microplastic pollution in the marine environment is a globally growing concern. Monitoring spatial distribution of microplastic concentrations, type, size and chemical composition may help to identify sources and entry pathways. Such information has crucial role in initiating focused mitigation. This study investigates microplastic pollution in marine surface waters of Latvia in order to understand the dynamics involved in microplastic spatial distribution. Surface water microplastic samples were collected in 45 transects during time period from May 2018 to September 2018 using Manta net (300 µm) that was attached to the side of the vessel in approximately 7 meter distance and trawled for 1 hour at speed of approximately 2 knots. Biological matter was digested using 10% sodium hydroxide, 15% hydrogen peroxide and enzymatic treatment. Next, samples were filtered on GF filter and visual examination was done under the microscope Leica DM400 B LED with camera DFC 295. Particles were analysed for their colour and size using image analysis, and each detected particle was affiliated to one of the six categories (fragment, filament, sphere, film, granule, foam). Identification of particle's chemical structure was done by Attenuated Total Reflection Fourier-transform infrared spectroscopy method using Thermo Fisher Scientific Nicolet iSO20 spectrometer. Microplastics were detected in all samples with concentrations ranging between 0.08 particles/m3 to 2.54 particles/m3. The greatest concentrations of particles were observed near costal recreational sites and river estuaries. Most of the particles belong to filament (53%) and fragment (41%) categories. From 3553 particles chosen for analysis of chemical structure 93% were plastic polymers. The most prevalent polymer types were polyethylene (68%) and polypropylene (13%). Research has been conducted with the support of Ministry of Environmental Protection and Regional Development Project No. IL/106/2017 “Improvement of knowledge of the state of the marine environment in the marine waters under the jurisdiction of Latvia”