The Toungoo–Mrauk-U War was a military conflict that took place in Arakan (present-day Rakhine State of Myanmar) from 1545 to 1547 between the Toungoo Dynasty and the Kingdom of Mrauk-U. The western kingdom successfully fended off the Toungoo invasions, and kept its independence. The war had a deterrence effect: Mrauk-U would not see another Toungoo invasion until 1580.
The war's origins can be traced back to 1542 when King Min Bin of Mrauk-U provided military support on the side of Ava in the Toungoo–Ava War (1538–45). Although Min Bin left the alliance in the same year, King Tabinshwehti of Toungoo was determined to repay the favor. In 1545, Tabinshwehti agreed to aid Min Aung Hla, the former Viceroy of Sandoway (Thandwe), who had been removed from office by Min Bin. In October 1545, Tabinshwehti sent a 4000-strong army but it was promptly driven back. Much larger Toungoo naval and land forces (combined 19,000 troops) tried again in the following dry season. The invasion forces overran southern Arakan, and were about to breach the defenses of the Arakanese capital Mrauk-U when Mrauk-U forces opened the sluices of the city's reservoirs, flooding the invaders out. On 30 January 1547, the two sides agreed to a peace treaty that allowed an orderly withdrawal of Toungoo forces from Arakan. The uneasy peace would last for the next 33 years.