The effect of acid marination on morphological changes in m. Longissinus dorsi during 48 hours acid marinating was studied. Muscles (48 h post mortem) were immersed in brine solution contained 2% sodium chloride and 2% sodium lactate and stored at 0 ± 4°C (meat pH after 48 hour marinating was 5,8). Control sample was kept in air conditions at 0 ± 4°C. Compared to untreated control, treated meat show higher marinade pick up and weight gain. Morphological observations during light microscopy demonstrated swelling of muscle fibers and increase in their diameter. Meat structure in acid marinated meat looks more homogenous due to strong effect of sodium lactate. Compared to control sample, connective tissue in acid treated meat was found clearly disordered. Sample preparations with Mayer‘s haematoxylin or Van-Gieson‘s picrofuchsin for light microscopy may be used effective for morphological observation of muscle and connective tissue changes during marinating.