The La1-xKxMnO3 perovskite-type oxides whose sizes were in nanometric range were prepared by the citric acid-ligated method. The structures of these perovskite-type oxides were examined by XRD and FT-IR. The catalytic activity for the combustion of soot particulate was evaluated by a technique of the temperature-programmed reaction. In the LaMnO3 catalyst, the partial substitution of K for La at A-site enhanced the catalytic activity for the combustion of soot particle. In the La1-xKxMnO3 catalysts, the combustion temperature of soot particle decreases with increasing x values. The La1-xKxMnO3 oxides with the substitution quantity between x=0.20 and x=0.25 are good candidate catalysts for the soot particle removal reaction, and the combustion temperature of soot particle is between 285 and 430 degrees C when the contact of catalysts and soot is loose, and their catalytic activities for the combustion of soot particle are as good as supported Pt catalysts, which is the best catalyst system so far reported for soot combustion under loose contact conditions.