The interaction between a peptide-based drug delivery system and two serum proteins, bovine serum albumin (BSA) and immunoglobulin G (IgG), is investigated using fluorescence quenching and calorimetric techniques. An ionic-complementary self/co-assembling peptide, EAR8-II, is employed to encapsulate the hydrophobic anticancer drug pirarubicin (THP) and stabilize it in protein environments. Self/co-assembling properties of the peptide-drug complex (EAR8-II-THP) are shown to be different while interacting with serum proteins compared with the properties of the isolated complex. The results from thermodynamic studies suggest that the drug delivery system has a strong binding affinity (K(SV) 1689 M(-1)), exothermic and enthalpy-driven interaction, with BSA and a relatively weak affinity with IgG (K(SV) 295.2 M(-1)). In the presence of salt ions, the enthalpy and binding affinity remain unchanged, implying other interactions such as hydrogen bonding and Van der Waals interactions are present that are not affected by reduced polarity. This work forms the basis for further studies of EAR8-II-THP complexes in the presence of important proteins and for further evaluation of the complexes' immune response and anticancer activity.