Abstract: Effect of Bacillus mucilaginosus preparation on the transform ation of potassium of soil mineral in pot mineralization test and field test and particularly the dynamics changes between available potasium and slow acting potasium in soils are reported in the article．Results show that adequate Bacillus mucilaginosus preparation applied in potasium deftcient soil increases the available potasium，up to 128．6％ in contrast to CK in jointing stage，and potasium adsorbed by plant，by 32．3％ more than CK ，due posibly to the release of the mineral potasium in soil by a special enzyme produced by Bacillus mucilaginosus．