This paper explores economic benefit for flood risk reduction of residents living in the core economic zones of lower Chao Phraya River Basin, Thailand. Under the action plan of integrated and sustainable flood mitigation in Chao Phraya River Basin, 4.29 million households would become beneficiaries. Using contingent valuation method (CVM), the potential benefit of flood risk reduction from this action plan is approximately THB 8.82 billion per year with an average willingness to pay (WTP) of THB 2,056 per household annually. The estimated benefit accrued to household residents in the study area is only part of the total potential benefits, if the plan were enacted. The finding reveals that household’s income, flood risk reduction, and program acceptance are significant determinants to increase WTP. Beneficiary pay mechanism such as flood protection fee or tax incorporating different income or different flood risk exposure on property should be considered in the flood management policy. This requires further studies on supporting regulations and laws.