Aqueous poly(urethane‐urea) dispersions were prepared by the prepolymer mixing technique without the use of any organic solvent. Most of the work focused on the use of two aliphatic diisocyanates (α,α, α', α'‐tetramethyl‐1,3‐xylylene diisocyanate and isophorone diisocyanate) and two macrodiols (α,ω‐poly(propylene glycol) (Mn = 1000) and α,ω‐poly(caprolactone) (Mn = 530)) in conjunction with a fixed proportion of emulsifying agent (dimethylol propionic acid, neutralized with triethyl amine) and the same chain extender (1,2‐ethylene diamine). The properties of both the dispersions and the dried polymer films, as well as those of some model prepolymers, were characterized as a function of the initial composition to establish criteria leading to the optimized performance in terms of dispersion stability and particle size and polymer properties. The most important parameter in this search was found to be the [NCO]/[OH] ratio, which gave the best results when it approached a value of 2.