Current theranostic approaches in cancer therapy demand delivery systems that can carry multiple drugs or imaging agents in a single nanoplatform with uniform biodistribution and improved target specificity. In this study, we have developed amphiphilized poly(ethyleneimine) nanoparticles (aPEI NPs) as a versatile multi-cargo delivery platform. The aPEI NPs were engineered to have the loading capacity for both hydrophobic molecules and negatively charged hydrophilic colloidal cargos through amphiphilic modification, i.e., octadecylation and subsequent PEGylation of poly(ethyleneimine). In the aqueous phase, the resulting aPEIs underwent amphiphilic self-assembly into spherical nanoparticles whose structure is constituted of the hydrophobic core with the positively charged surface and the hydrophilic neutral corona. The high degree of PEGylation resulted in the tiny colloidal size (<15 nm in diameter) and rendered the outmost surface coated with an antifouling corona which minimizes general shortcomings of poly(ethyleneimine)-based nanocarriers (e.g., cytotoxicity and liver filtration) while keeping its advantage (loading capability for negatively charged drugs). The unique nanostructure of aPEI NPs allowed for facile loading of hydrophobic model drugs (rubrene and IR780) in the core as well as negatively charged colloids (Pdots, proteins and DNA) on the inner surface via the hydrophobic and electrostatic interactions, respectively. Fluorescence imaging experiments demonstrated that the highly PEGylated aPEI-25 NPs showed prolonged blood circulation with minimal liver filtration and efficient delivery of the loaded cargos to the tumor. These combined merits, along with negligible toxicity profiles both in vitro and in vivo, validate the potential of aPEI-25 NPs as versatile nanocarriers for multi-cargo delivery.