An organic silicon compound is obtained by hydrolyzing (A) a hydrolyzable silane containing an alkoxy or acyloxy group and a nitrogenous organic group: and (B) a hydrolyzable silane containing an alkoxy or acyloxy group. The hydrolyzate or organic licon compound is available as an aqueous solution which is ready for use as a binder composition. An aqueous coating composition comprising the binder composition and optionally, a UV screen compound is also provided. The binder composition and the coating composition are shelf stable and impart water resistance, heat resistance and weatherability.