Highly weathered coal debris and peats were pulverized into fine powders. They contain humic acid ranging from 30-50%. Effects of the rate of mobilizing phosphorus from rock phosphate powders by these humified materials were studied in incubated culture, pot experiments and field experiments. Results obtained are summarized as follows. 1. The acidity of pure humic acid was adjusted to pH 4.2-7.1. The humic acid solutions were mixed with powdered rock phosphate in culture dishes and incubated at 29±1℃ for two weeks. Rate of liberation of phosphorus from Kai-yang rock phosphate, a fluor-apatite containing 35% P₂O₅, was about 6-17% of the theoretical value of the hydroxyl group of humic acids. It increased with the increase of acidity of the humic acids. Powdered rock phosphates were also cultured with coal powders. In this regard, the rate of liberation of phosphorus from the rock depends upon the content of humia acid in the weathered coals.