In cancer chemotherapy, core-cross-linked particles (CCPs) are a promising drug carrier due to their high structural stability in an in vivo environment, resulting in improved tumor delivery. A biocompatible polymer of polyethylene glycol (PEG) is often utilized to coat the surface of CCPs to avoid nonspecific adsorption of proteins in vivo. The PEG density and conformation on the particle surface are important structural factors that determine the in vivo fate of such PEGylated nanoparticles, including their pharmacokinetics and pharmacodynamics. However, contrary to expectations, we found no significant differences in the in vivo pharmacokinetics and pharmacodynamics of the PEGylated CCPs with the different PEG densities including mushroom, brush, and dense brush conformations. On the contrary, the in vivo release kinetics of hydrophilic and hydrophobic model drugs from the PEGylated CCPs was strongly dependent on the PEG conformation and the drug polarity. This may be related to the water-swelling degree in the particle PEG layer, which promotes and inhibits the diffusion of hydrophilic and hydrophobic drugs, respectively, from the particle core to the water phase. Our results provide guidelines for the design of cancer-targeting nanomedicine based on PEGylated CCPs.