The synthesis and the aggregation behavior of novel well-defined poly(N,N-diethylacrylamide)-b-poly- (L-lysine) (PDEAm-b-PLL) double hydrophilic block copolymers are reported. PDEAm-b-PLL was prepared using an original strategy which consisted of the ring opening polymerization (ROP) of N3- trifluoroacetyl-L-lysine N-carboxyanhydride using terminated-thiol PDEAm as a macroinitiator. After deprotection of the amine group of the L-lysine, pH- and thermo-sensitive poly(N,N-diethylacrylamide)- b-poly(L-lysine) block copolymers were obtained. The structure of the copolymers was characterized by 1H NMR and FT-IR. Then, pH and temperature sensitivities were measured by 1H NMR and UV/Vis spectroscopy. At different pH values and temperatures, poly(L-lysine) and poly(N,N-diethylacrylamide) showed typical behaviors, which led to different types of aggregation in aqueous solution. The influence of both stimuli was carefully investigated by DLS, TEM, and SANS.