The mechanical properties of tissues and cells are increasingly recognized as an important feature for the understanding of pathological processes and as a diagnostic tool in biomedicine. Impulsive stimulated Brillouin scattering (ISBS) is promising to overcome shortcomings of other measurement methods such as invasiveness, low spatial resolution and long acquisition time. In this paper, we present for the first time ISBS measurements of hydrogels, which are model materials for biological samples. We demonstrate ISBS measurements discriminating hydrogels of different stiffness. ISBS measurements with lateral resolution close to cellular level are presented. These results underline that ISBS microscopy has a high potential for biomedical applications.