To provide a tackifying resin emulsion having such excellent light resistance that a tacky adhesive is neither yellowed nor embrittled even when exposed to ultraviolet light irradiation for a long time and to provide a water-based tacky adhesive composition.

The tackifying resin emulsion is obtained by emulsifying esterified rosins (A) which have ≤0.15 maximum absorbance A in a range of ≥254 nm when measured by ultraviolet absorptiometry (measurement conditions: the sample concentration is 1 g/dm3 and the length of a cell is 1 cm) and in which the content of a component having 320 molecular weight of a methylated hydrolyzate thereof measured by a gas chromatograph mass spectrometer is ≥95% of the total content of components having 314-320 molecular weight. The water-based tacky adhesive composition contains the tackifying resin emulsion.