Results of the research into the application of ultrasound waves to develop meat quality point out that it induces changes in physicochemical properties of tissue, in particular water-protein interactions. The objective of this study was to assess the impact of ultrasound treatment of pork meat showing PSE features during the rigor mortis period (24 h after slaughter) on the conformational changes in proteins of myofibre as reflected by changes in the surface hydrophobicity and ultrastructure of muscle fibre sarcomere. The research was performed using a pork meat (m. biceps femoris – thigh biceps muscle) taken from carcasses chilled to 7 °C for 24 h. On the basis of the pH and L* parameter (L*a*b* colour space), the muscles were classified either as PSE or as normal. One of the PSE muscles constituted a control sample (K – PSE sample) whereas the other was treated in an ultrasound field with a frequency of 45 kHz (U45 – PSE sample). Upon sonication, the meat samples were stored at 4°C for 96 h after slaughter. The scope of analysis comprised: determining meat acidity, assessing ultrastructure, and measuring hydrophobicity of isolated myofibrillar proteins. It was proved that the normal muscles (N sample) were characterized by higher pH values than the muscles of K-PSE and U45-PSE samples during the whole period after slaughter. At the beginning of the experiment, the lowest value of surface hydrophobicity was reported in the U45 – PSE sample. The proteins of the meat samples investigated were characterized by the largest hydrophobic surface (about 90 %) 48 h after slaughter. During the further storing of meat, the value of the feature studied decreased. The results obtained prove that the ultrasound treatment has a secondary impact on the transformations of myofibrillar proteins. The water – myofibrillar protein interaction, counted among surface properties, constitutes a reflection of those transformations.