In order to assess the behavior of ceramic fibers that are respired and accumulate in the lung, the solubility of bio-soluble CaO-MgO-SiO2 system ceramic fibers was determined by measuring the concentrations of the main components in the Gamble solution after different solution periods. The effect of ZrO2, TiO2, B2O3, Al2O3 and the different CaO/MgO ratio of fibers on the solubility of the ceramic fibers were investigated. The results indicated that the pH value of the Gamble solutions increase with the increasing of solution time. CaO, MgO, SiO2 in the ceramic fiber have greater solubility. The existence of ZrO2 and Al2O3 in the fibers would reduce the solubility of the fibers, and the existence of TiO2, and B2O3 in fibers will benefit the solubility of the fibers.