Novel organic silicon compounds having a UV absorbing benzotriazole or benzophenone skeleton are provided comprising R¹₃SiO 1/2 and SiO₂ units as essential units, 0 to 20 mol% of R²SiO 3/2 and R³₂SiO units, and 0 to 20 mol% of R³₂SiO units. The siloxane units are present in a molar ratio: (R¹₃SiO 1/2 + R²SiO 3/2 + R³₂SiO)/SiO₂ of from 0.5 to 1.5. A benzotriazole or benzophenone-bearing group constitutes 1 to 33 mol% of the total quantity of the organic groups represented by R¹, R² and R³ while the remainder is a monovalent saturated or unsaturated organic group or groups having 1 to 18 carbon atoms. Cosmetic compositions containing the same compounds have improved UV absorbing capacity.