We found that BA-j as a substrate compound for ATP can directly inhibit the activity of CDK1 studied by FRET which is the enzyme activity determination method of the CDK1 in non-cancer cells, and the inhibitory activity of BA-j (CC50 0.30 μM) against CDK1/Cyclin B1 is approximately 20-fold and 50-fold stronger than BA and Baicalin. Here, CDK1 is linked to cancer.