Biocompatible polymers have been of considerable interest in developing drug delivery systems (DDSs). However, physicochemical characterizations of the polymers and DDSs had been limited because of the difficulty in obtaining the same synthesized copolymers and achieving a similar drug loading ability with the differing properties of the drugs. Therefore, a correlational study of the relationships between copolymers and DDSs was required to estimate the properties of the DDSs and to develop optimal systems of delivery depending on the drug. In this study, we presented several relationship correlation equations of physicochemical properties and copolymers according to their molecular weights (MWs) using amphiphilic block copolymers composed of poly(L-lactide)-block-methoxy-poly(ethylene glycol) (PLA-b-mPEG). The PLA-b-mPEG was characterized by nuclear magnetic resonance and gel permeation chromatography, and the critical micelle concentration (CMC), sizes, and drug loading capacity (DLC) of the self-assembling micelles from the copolymers with different MWs were all measured. The increase in MW of the PLA led to a decrease in CMC and DLC with an increase of the particle sizes. The relationship between the MW of the PLA and the physicochemical properties of the micelles demonstrated a good correlation, which provides excellent information for the use in the development of tailor-made DDSs based on copolymers pursuing optimal particle size, DLC, CMC, and so on.