This paper examines the limitations of the Chiang Mai Initiative Multilateralization (CMIM) as a regional financial safety net in East Asia, and proposes a new regional financial arrangement. To overcome the drawbacks of the CMIM, which has never been activated so far, a new regional financial arrangement suggests that ASEAN+3 members establish a regional reserve system based on a supranational regional reserve asset. The new regional financial arrangement, so-called “Reserve Liquidity Line” (RLL), guarantees a degree of automaticity in liquidity facility, based on upfront funding instead of pledge funding. As a backdrop of the regional reserve system, some market movements have been manifested to reduce excessive U.S. dollar dependency in East Asia and to enhance the use of local currencies. Establishing the RLL mechanism could find a way of making up for the weak points of the CMIM and responding to the regional needs for effective regional financial arrangements. The proposed operational mechanism of RLL comprises (i) institution building of ASEAN+3 Reserves System (ARS) to manage the Regional Reserves Asset (RRA), (ii) an Operations Account and a Substitution Account, and (iii) a sort of basket exchange rate for RRA valuation.