Potassium is the most abundant nutrition element in the surface soil but most of the potassium is unavailable to the plants. The present study was conducted with the aim of isolation of potassium solubilizing bacteria from rhizosphere soil and evaluation of quantitative ability of released potassium from different sources of silicate by strains. For this propose, laboratory and greenhouse evaluations were carried out on corn (Zea mays L. Cv. single cross 640 (as a factorial in a completely randomized design with three replications. Laboratory factors were potassium sources (four levels), incubation time (seven levels) and microbial inoculation (six strains) and greenhouse factors were potassium sources (five levels) and microbial inoculation (four strains). The results showed that among the bacterial strains KSB₁₃ had maximum dissolution diameter (25 mm) and solubilisation index (SI=3). The highest potassium content (3/32 µg/mL) was released from biotite by strains of KSB₁₀ after ten days incubation. The microbial inoculation increased root dry weight and plant height for 30 and 25 percent, respectively, compared to control treatments. Also the mean shoot dry weight and K content in microbial treatments of silicate minerals were respectively increased 3/75 and 1/57 times higher than control treatment. It can be concluded that microbial inoculation causes potassium release from silicate minerals and improved plant growth.