Laboratory tests were conducted to evaluate the influence of slenderness on the performance of fibre reinforced polymer (FRP) standing supports subject to uniaxial compression. The FRP standing support consist of external FRP tube and internal infill cylinder made of coal rejects and cementitious grout. 21 cylindrical specimens with diameter of 100 mm and various heights ranging from 200 mm to 600 mm were prepared and tested. Test results indicated that all FRP standing supports exhibited strain hardening yielding. While the strength of the FRP standing supports stabilized at around 47 MPa when their height to diameter (h/d) ratio was not greater than 5, it declined by approximately 13% when the h/d ratio was 6. The strain at peak strength of the FRP standing supports generally decreased as the h/d ratio increased, dropping from 3.57% at the h/d ratio of 2 to 2.16% at the h/d ratio of 6.