PURPOSE: To provide an aqueous binder dispersion used for a base lacquer coating of a multilayer coat having hardness and water resistance and a coating composition containing the same.

CONSTITUTION: There is provided an aqueous binder dispersion containing (A) 45-95 wt.% at least one polyurethane being in the form of an aqueous dispersion and obtained by effecting the free radical initiated polymerization of a polyurethane macromonomer containing carboxylic, phosphonic and/or sulfonic groups and lateral vinyl groups in the presence of a monomer copolymerizable with the polyurethane macromonomer and (B) 5-55 wt.% polyurethane resin being in the form of an aqueous dispersion and having an Mn of 10,000-300,000 and an acid value of 5-50 and containing neither a urea group nor a carbonate group and obtained by chain-extending a polyurethane prepolymer having an OH value of 5-75 and an Mn of 500-50,000 by reaction with a polyfunctional isocyanate having a free-NCO functionality of at least 1.8 and used in an amount to give a desired Mn to the product.