We synthesize various substituted triazole-containing flavonoids and identify potent, nontoxic, and highly selective BCRP inhibitors. <b>Ac18Az8</b>, <b>Ac32Az19</b>, and <b>Ac36Az9</b> possess <i>m</i>-methoxycarbonylbenzyloxy substitution at C-3 of the flavone moiety and substituted triazole at C-4' of the B-ring. They show low toxicity (IC<sub>50</sub> toward L929 > 100 μM), potent BCRP-inhibitory activity (EC<sub>50</sub> = 1-15 nM), and high BCRP selectivity (BCRP selectivity over MRP1 and P-gp > 67-714). They inhibit the efflux activity of BCRP, elevate the intracellular drug accumulation, and restore the drug sensitivity of BCRP-overexpressing cells. Like Ko143, <b>Ac32Az19</b> remarkably exhibits a 100% 5D3 shift, indicating that it can bind and cause a conformational change of BCRP. Moreover, it significantly reduces the abundance of functional BCRP dimers/oligomers by half to retain more mitoxantrone in the BCRP-overexpressing cell line and that may account for its inhibitory activity. They are promising candidates to be developed into combination therapy to overcome MDR cancers with BCRP overexpression.