CDK9/10/GSK3β-IN-1 (compound 13c) is a kinase inhibitor ( Flavopiridol analogue) that effectively inhibits HsGSK3β ( IC 50 =59 nM), HsCDK9/CyclinT ( IC 50 =64 nM), HsCDK5/p25 ( IC 50 =1.093 μM) and HsCDK2/CyclinA ( IC 50 =1.725 μM). CDK9/10/GSK3β-IN-1 has anti-cancer cellular activity comparable to or higher than that of Flavopiridol. CDK9/10/GSK3β-IN-1 shows high anti-proliferative activity in vitro against up to seven cancer cell lines.