The effect on litter decomposition rates was studied after annual additions for four years to the forest floor of sulfuric acid (64 kg S.ha−1), sulfur powder (64 kg S.ha−1), and in the first year limestone (dolomite) powder (412 kg Ca+230 kg Mg.ha−1). The litter was Norway spruce needles which were incubated in the field in litter‐bags. Drastic reductions in decomposition rates were observed and the addition of diluted acid caused a rate reduction to 66%of that in control and the additions of sulfur powder a reduction to 80%. The effect of the sulfur powder on litter mass‐loss rate appeared to be delayed and could not be noted until one year after the first addition. No effect could be seen of the limestone powder.