Abstract: Zooplankton is an important part of Baltic ecosystem and ecosystem-based management requires productivity assessment of the region what involves zooplankton identification and abundance estimation. Acoustics is recognized as a reliable monitoring method. Thus, the ability of understanding of backscattering by zooplankton becomes a priority. It was the main motivation of the paper. The main approach is based on (i) the numerical modeling of acoustic backscattering by the typical representative of Baltic zooplankton, mysids and (ii) comparison of the theoretical results with the measured acoustic data. The Modal Based Deformed Wave Born Approximation (MB-DWBA) model was employed. The readily available biologic data for mysids were used. The sensitivity of the backscattering to acoustic frequency, individual size, width of orientation distribution and acoustic properties of biologic tissue was analyzed. The results of modeling were verified using the measured acoustic and biologic data collected in August 2003 in the Swedish coastal zone near Stockholm.