In study of the behaviour of roof strata in underground coal mines the strength of the roof rock, particularly, the unconfined compressive strength (UCS) plays a significant role. Application of simple tools in assessment of the rock strength has been practiced by many researchers one of which being Schmidt hammer. Due to its portability, easiness in use, rapidity, low cost and its non-destructive procedure of application, it is among the most popular tools in this respect. Application of this tool in prediction of the roof rock strength, in a new context, is the aim of this research work. A comprehensive review of the literature revealed that most of the empirical equations introduced for determination of the unconfined compressive strength of rocks based on the Schmidt hammer rebound number (Rn) are not practically reliable enough as in most of the cases one formula is used for all types of rocks, although the density of rocks is introduced to the formulas in some of these cases. On the other hand, if one specific relationship between hammer rebound number and unconfined compressive strength is introduced for one type of rock, the equation will yield a much higher coefficient of correlation. During a research program supported by The Shahrood University of Technology, Iran, a third type of approach was considered. The study aimed to express the relationship between Schmidt rebound number and unconfined compressive strength of rock mass under a particular geological circumstances. As an example, in this study, the situation selected was the immediate roof rock of coal seams at Tazareh Colliery, Shahrood, Iran. In order to determine the Schmidt number and the unconfined compressive strength, a significant number of samples were selected and tested both in-situ and in the laboratory and a new relationship was introduced. The equation can be used to predict UCS of the roof rock in coal extracting areas at this colliery by performing simple in-situ Schmidt hammer tests.