Advanced Mo-based Rare process Experiment (AMoRE) – II led by Center for Underground Physics (CUP) will search for neutrinoless double beta ($0v\beta\beta$) decay of $^{100}$Mo, using molybdate crystals such as $^{40}Ca^{100}MoO_3$ (CMO) crystals [1]. Because the theorized 0νββ decay would happen rarely, it is important to reach zero-background level around the region of interest near 3 MeV. Therefore, it is necessary to check the raw material of the crystal, the $^{100}MoO_3$ powder, for trace levels of radioactive contamination. The High Purity Germanium (HPGe) detector group operates an array of 14 HPGe detectors, referred to as CUP Array of Germanium (CAGe), at the YangYang underground Laboratory (Y2L) in Korea. By measuring $^{100}MoO_3$ powder samples in the CAGe, we obtained activity levels of $^{226}$Ra (1.6 ± 0.3 mBq/kg), $^{40}$K (12 ± 3 mBq/kg), 228Ac (344 ± 71 $\mu$Bq/kg), $^{228}$Th (244 ± 50 $\mu$Bq/kg), and $^{88}$Y(33 ± 8 $\mu$Bq/kg). Data analysis and experimental methods are discussed in this report.