We report self-assembling polymer cubicles prepared by poly(e-L-lysine) conjugated to lactobionic acid and pentanoic anhydride (PKLC5). The lactobionyl and pentanoyl groups provide hydrophilic and hydrophobic properties, respectively, while the amine group unreacted provide pH-sensitivity to the polymer. As the pH decreased from 10 to 6, the aqueous polymer solution exhibited transparent-turbid-transparent transition. Scanning electron microscopy revealed that the polymer became turbid and form cubic nano-micro particles at pH=8. We hypothesize that the hydrophobic pentanoyl groups drive the aggregation, and optimal hydrogen bonding of the functional groups in a specific direction at pH=8 leads to cubicle formation. To identify the cubicle formation at pH=8, X-ray diffraction, dynamic light scattering, zeta potential, 2D-NMR, FTIR, and CD spectroscopies of the aqueous polymer solutions were studied.