A Thin Spray-on Liner (TSL) is defined as a chemically based layer or coating (3-5 mm) that is sprayed onto the rock surface to support mining excavations (Saydam and Docrat, 2007). Since the introduction, TSLs have received success in some applications in hard rock mines; however, their use has been slow in coal mining. The adhesion strength between a TSL and a rock surface is an important parameter controlling the design and performance of liner support systems. The in situ adhesion tests have been conducted to study the bonding between a TSL material and the coal substrate in an underground coal mine in NSW. A direct pull-off adhesion tester was adopted to conduct adhesion tests on the ribs of the roadway. In this paper, the in situ adhesion test results on coal substrate are analysed and presented.