The support of underground mine drift is an essential task in mine operations as the safety of mining operations and especially workers, affect the effectiveness of productions due to delays and accidents. It is desirable that mine companies pay attention not only to the support designs but also the reliability of those designs. The uncertainties in the support design parameters affecting the probability of failure are not taken into account in deterministic analysis of the factor of safety which gives only a partial representation of the true margin of safety. Hence, this paper investigates the extent of the probability of failure of the rock supporting elements in underground mine through a reliability assessment. The rock support design data used in Ridder-Sokolny mine, East Kazakhstan are employed as case studies. A methodology based on the well-known Q-system combined with numerical simulation and the first order reliability methods (FORM) was implemented. Four cases of support were considered namely: unsupported excavations, rock bolting, concrete and concrete and bolting combined. For each of them, the factors of safety, reliability index and probability of failure were determined in accordance with the corresponding rock mass quality and excavation geometry. The estimated probability of failure of the support ranged between 0.31% and 38% depending on the rock conditions and the type of support. Overall, the results indicated that the probability of failure of the support increases with a decrease of the Q values. Meanwhile, the factor of safety also increases with a decrease of the width/height ratio of the excavations. These results are in good agreement with cases of failed support systems observed in the mine. It is concluded that the results could serve as basis to readjust the support design, especially for those with high probability of failure.