AIM: The aim of this study was to determine cytotoxic activity of BornUSU I or Boronhafagama I (1,5-bis(4-hydroxyphenyl)-3-oxa-1,5-diaza-2,4-diboropentane-2,4-diol) as a boron derivate compounds which are boron neutron captured theraphy (BNCT) candidates. METHODS: The T47D cells were treated by BornUSU I, and Tamoxifen as a positive control. The in vitro study was using MTT method with the incubation period for 24h and 48h. All data were determined using viability of cells equation for showing each IC50 value. RESULTS: The IC50 value of BornUSU I and Tamoxifen were 72.61 ± 0.82 µM and 10.62 ± 0.06 µM for 24 h incubation period, and for the 48 h incubation period were 44.63 ± 0.23 µM and 7.79 ± 0.05 µM. The 48 h incubation period results showed the lowest IC50 value. CONCLUSION: The results reveal that BornUSU I provide effective as anticancer, especially for breast cancer treatment.