Various soil amendments were investigated in a field experiment to revegetate a surface coal mine in Vietnam. The effect of power station ash, charred rice straw and fine material from the mine on soil chemistry, soil enzyme activities and plant growth was tested. Enzymes evaluated were β-glucosidase, urease, acid and alkaline phosphatase, arylsulphatase, catalase, arginine ammonification and fluorescein diacetate hydrolysis. Due to the small amount of amendments, applied for economic reasons, and nutrient leaching during periods of high precipitation, only acid phosphatase activity was affected by treatments after four months. Plant height after 1.5 years was not found to be affected. We conclude that for monitoring soil quality of acid, P-deficient substrates from subtropical surface coal mines, the activity of acid phosphatase may be a useful bioindicator.