To obtain the subject composition free from occurrence of crack of coating film even when subjected to thick coating, excellent in coating film processability and room temperature curable property and useful for coating film, etc., lowering nitrogen oxide concentration of automobile discharge gas by using a specific polycondensation product of organosilicon as a binder.

This coating composition comprises (A) powder having photocatalyst activity and selected from titanium dioxide powder and zinc oxide powder (e.g. anatase type titanium dioxide powder) and (B) a polycondensation product of organosilicon obtained by hydrolyzing a mixture of a compound of formula I (R is a 1-8C hydrocarbon group) or its oligomer with a compound of formula II (R' is a 1-12C hydrocarbon group) or its oligomer in the presence of an acid catalyst and condensing the hydrolyzate at pH≥7. The coating composition contains preferably 5-65 pts.wt. component A in 100 pts.wt. total solid content.