The paper presents the test results of the shear strength of composite materials, in which the base material was peat. The materials modifying the mineral part of the peat ground skeleton were fly ash and hydrated lime. The research was carried out for two groups. In group 1, the ratio of the mass of the peat skeleton to the mass of fly ash was equal to one, and in group 2, it was two. Hydrated lime content in the unit mass of the composite in group 1 was 2.4, 4.8 and 9.2%. In the second group, it was 1.6, 3.2 and 6.4%. The test results showed that the materials from group 1. (P/FA = 1) are characterised by the highest shear strength compared to materials from group 2. (P/FA = 2), regardless of the content of hydrated lime. It should also be noted that the shear strength of the materials of group 1 was significantly higher than the shear strength of the base material, which was peat.