The cytotoxic effect of boron neutron capture therapy (BNCT) is due to the nuclear reaction between 10B and thermal neutrons. Recently, polyethylene glycol (PEG) has attracted attention due to its ability to avoid uptake by reticulo- endothelial systems, and to accumulate in the tumor cells. We prepared boronated PEG-binding bovine serum Albumin (BSA). Prompt g-ray spectrometry showed that 250.0 +/- 4.9 ppm 10B atoms were found to conjugate to PEG-BSA. 10B concentrations in AsPC-1, human pancreatic cancer cells obtained 0, 9, 24 hrs after incubation with 10B- PEG-BSA were 0, 4.97 +/- 0.49, and 13.01 +/- 1.74 ppm respectively. It is said that the 10B concentrations between 15 and 30 ppm are necessary for effective boron neutron-capture therapy. These data indicated that the 10B-PEG-BSA were getting close to the lowest acceptable limit of 15 ppm, and when using Na210B20H18 and increasing the 10B binding site of the BSA, we could increase the 10B uptake levels in the tumors for BNCT.