Surfactant-free waterborne hybrid alkyd–acrylic dispersions with a solid content of 40% were synthesized, characterized and their long term stability investigated. Spontaneous emulsification of the ensuing hybrid resin was achieved, following the addition of base aqueous solution such as NH3, triethylamine (TEA) or NaOH that neutralize the carboxyl groups. The key role of the carboxylic groups in the stabilization process was discussed and the effect of their content on the properties of the dispersion was analyzed. According to the neutralizing base, the particle size of the dispersion, its viscosity and the hydrolytic resistance of the hybrid resin were greatly altered.