Stability and narrow size distribution are among the main requirements that apply to drug formulations based on polymeric nanoparticles. In this study, we obtained a series of particles based on biodegradable poly(D,L-lactide)-b-poly(ethylene glycol) (P(D,L)LAn-b-PEG113) copolymers with varied hydrophobic P(D,L)LA block lengthnfrom 50 to 1230 monomer units stabilized by poly(vinyl alcohol) (PVA) by a simple “oil-in-water” emulsion method. We found that nanoparticles of P(D,L)LAn-b-PEG113copolymers with relatively short P(D,L)LA block (n≤ 180) are prone to aggregate in water. P(D,L)LAn-b-PEG113copolymers withn≥ 680 can form spherical unimodal particles with values of hydrodynamic diameter less than 250 nm and polydispersity less than 0.2. The aggregation behavior of P(D,L)LAn-b-PEG113particles was elucidated in terms of tethering density and conformation of PEG chains at the P(D,L)LA core. Docetaxel (DTX) loaded nanoparticles based on P(D,L)LA680-b-PEG113and P(D,L)LA1230-b-PEG113copolymers were formulated and studied. It was observed that DTX-loaded P(D,L)LAn-b-PEG113(n= 680, 1230) particles are characterized by high thermodynamic and kinetic stability in aqueous medium. The cumulative release of DTX from the P(D,L)LAn-b-PEG113(n= 680, 1230) particles is sustained. An increase in P(D,L)LA block length results in a decrease in DTX release rate. The in vitro antiproliferative activity and selectivity studies revealed that DTX-loaded P(D,L)LA1230-b-PEG113nanoparticles demonstrate better anticancer performance than free DTX. Favorable freeze-drying conditions for DTX nanoformulation based on P(D,L)LA1230-b-PEG113particles were also established.