Zwitterionic polymers exhibit strong hydration, high biocompatibility, and antifouling properties. Dendrimers are regularly branched polymers, which are used in the drug delivery system (DDS). In this study, we synthesized zwitterionic monomer- and polymer-conjugated dendrimers as a biocompatible nanoparticle to investigate the relation between the hydration property and biodistribution. A sulfobetaine monomer (SBM) was conjugated at the termini of the polyamidoamine (PAMAM) dendrimer. Polysulfobetaines (PSBs) were produced by reversible addition-fragmentation chain transfer polymerization and were also conjugated at the termini. Intermediate water, that is, water molecules loosely bound to the material, can be estimated from the melting peaks at less than 0 °C in differential scanning calorimetry (DSC) measurement. Our DSC results showed that the PSB-conjugated dendrimers (PSM-dens) contained more intermediate water than the SBM-conjugated dendrimer (SBM-den). PSB-dens accumulated in the tumor after intravenous administration, but SBM-den did not. These suggested that the amount of intermediate water, that is, the hydration property, was related to the biodistribution of the zwitterionic dendrimers. This relation is a possible design criterion for drug carriers. PSB-dens accumulated in the tumor even after the second injection, possibly overcoming the accelerated blood clearance observed with poly(ethylene glycol)-modified nanoparticles. Thus, this kind of zwitterionic polymer-conjugated dendrimer is useful for the DDS in cancer treatment.