The rock mass and material properties, in-situ stress, discontinuities, and the excavation technique used all influence the stability of the galleries span in underground mines. Many underground mines have galleries that excavation span both with and without support (wooden support, steel bond, rock bolt, shotcrete, etc.). The strength of the rock units in the galleries span in the bedrock in a lead-zinc underground mine located in Yahyali district of Kayseri province, as well as the durability without and with support, were investigated in this study. Representative samples were taken from the main galleries, 32, 55, 67, and 90 floors for both the features determining the RMR parameters and the rock mechanics laboratory experiments. As a result of the evaluations, it was determined that the galleries on the 32^nd, 55^th, and 67^th floors of the limestone unit can be stable without support for at least 10 years at excavation spans of 3.8 m, 3.9 m, and 3.7 m, respectively. Furthermore, the schist unit on the 67^th floor was found to be stable for one year up to a 2.9 m excavation span, and the schist unit on the 90^th floor was found to be stable for 1.5 years up to a 3.1 m excavation span.