It is necessary to accumulate the B-10 atoms to the tumor cells selectively for effective boron neutron capture therapy(BNCT). In order to achieve on accurate measurement of B-10 concentrations in biological samples, we employ a technique of neutron capture autoradiography(NCAR) of the sliced whole body samples of tumor bearing mice using CR-39 plastic track detectors. The CR-39 detectors attached with samples were exposed to thermal neutrons in the thermal column of the TRIGA II reactor at the Institute for Atomic Energy, Rikkyo University. We obtained NCAR images for mice injected intraveneously by B-10-polyethyleneglycol(PEG) binding liposome or B-10-bare liposome. The B-10 concentrations in the tumor tissue of mice were estimated by means of alpha-track density measurements. In this study, we can increase the accumulation of B-10 atoms in the tumor tissues by binding PEG chains to the surface of liposome, which increase the retension in the blood flow and escape the phagocytosis by reticulo-endotherial systems. Therefore, B-10-PEG liposome will be a candidate for effective B-10 carrier in BNCT for cancer.