An automobile body-used light-colored water based coating composition containing a water dispersion (A.sub.1) prepared by water-dispersing a block copolymer resin (A) comprising a copolymer (a.sub.1) obtained by copolymerizing a monomer component containing an olefin monomer and a copolymer (a.sub.2) obtained by copolymerizing a monomer component containing a carboxyl group or carboxylic anhydride group-containing vinyl monomer, a hydroxyl group-containing resin (B), a curing agent (C) and a color pigment, a resulting coating film having a lightness L* value in accordance with a L*a*b* color system as defined in JIS Z 8729 in the range of 80 or more.