Protein-based nanomedicine plays an important role in tumor chemotherapy due to their merits in bioavailability, biocompatibility, biodegradability, and low toxicity. In this study, we developed a novel method of preparing human serum albumin (HSA) nanoparticles for targeted delivery of paclitaxel (PTX) to tumors. HSA-PTX nanoparticles (NPs-PTX) were fabricated via unfolding of HSA in appropriate solution to expose more hydrophobic domains and consequent self-assembling into nanoparticles with added PTX. Via this self-assembly method, a desirable particle size (around 120 nm), a high drug loading (>20%), and a high encapsulation efficiency (near 100%) were obtained. PTX dispersed as an amorphous state in NPs-PTX and the secondary structures of HSA were maintained. In a cytotoxicity study, NPs-PTX displayed an enhanced cytotoxicity in MCF-7 and A549 cells. Confocal microscopy and flow cytometry revealed that the uptake of NPs-PTX was mediated by secreted protein acidic and rich in cysteine and "caveolar" transport. In H22 tumor-bearing mice, NPs-PTX displayed an increasing and everlasting tumor distribution, leading to slower tumor growth and longer mice survival than PTX. Therefore, this novel self-assembly method offers a much easier method to prepare PTX nanoparticles, provides better antitumor efficacy in vitro and in vivo, and more importantly, sets up a delivery platform for other hydrophobic drugs to improve their effectiveness in cancer therapy.