β-sitosterol/poly(ethylene glycol)-block-poly(lactic acid) (PLA-b-PEG) complexes were prepared by solution blending in purified water and ethanol. The mixture of water and ethanol is a suitable solvent system for the two components. The complex was studied by using Nuclear Magnetic Resonance (NMR) spectroscopy and Differential Scanning Calorimetry (DSC). β-sitosterol is a drug that may reduce the swelling of benign prostatic hyperplasia (BPH) and diminishing inflammation. However, it is hydrophobic and difficult to deliver in aqueous solution. Since PLA-b-PEG has amphiphilic properties, the complex described here may enhance delivery of this drug for treatment of BPH. Proton NMR (1HNMR) of the complexes shows that the methylene (CH2) protons of the PEG, the (-O-CH-) of PLA, and (CH3) of PLA are slightly shifted because of its non-covalent interaction with β-sitosterol. The complex formation was supported by 2-D NMR (NOESY) spectroscopy. NOESY spectra show cross peaks, indicating the interaction between the two components. DSC of the complexes shows thermal characteristics that are different from the individual components. In particular, the PEG in the complex shows a lower melting point and decreased crystallinity compared to the pure PEG. The melting point is lowered from 57°C to 55.3 °C for the PEG-b-PLA/β-sitosterol (5%) complex. Under the same condition, the melting point of PLA dropped from 170 °C to 130 °C. Atomic force microscopy shows changes in the surface morphology of the copolymer from crystalline to amorphous when incorporated with the drug. NMR, DSC, AFM, and MTT assay studies suggest the formation of a relatively stable β-sitosterol/poly(lactic acid)-block-poly(ethylene glycol) complex. The cell proliferation assay (MTT assay) suggests significant inhibition of the stimulation of growth of prostate cancer cells upon addition the complex.