The Toungoo–Ava War (1538–1545) is a military conflict that takes place in present-day Lower and Central Burma (Myanmar) between the Toungoo Dynasty, and the Ava-led Confederation of Shan States, Hanthawaddy Pegu and Arakan (Mrauk-U).

Toungoo's decisive victory gives the upstart kingdom control of all of central Burma, and cements its emergence as the largest polity in Burma since the fall of Pagan Empire in 1287.

The war begins in 1538, when Ava, through its vassal Prome, throws its support behind Pegu in the four-year-old war between Toungoo and Pegu.

After its troops break the siege of Prome in 1539, Ava gets its Confederation allies agreed to prepare for war, and forms an alliance with Arakan, but the loose alliance crucially fais to open a second front during the seven dry-season months of 1540–41 when Toungoo is struggling to conquer Martaban (Mottama).The allies are initially unprepared when Toungoo forces renew the war against Prome in November 1541.

Due to poor coordination, the armies of the Ava-led Confederation and Arakan are driven back by better organized Toungoo forces in April 1542, after which the Arakanese navy, which has already taken two key Irrawaddy delta ports, retreats.

Prome surrenders a month later.

The war now enters an eighteen-month hiatus during which Arakan leaves the alliance, and Ava undergoes a contentious leadership change.

In December 1543, the largest army and naval forces of Ava and the Confederation come down to retake Prom, but Toungoo forces, which have now enlisted foreign mercenaries and firearms, not only drive back the numerically superior invasion force but also take over all of Central Burma up to Pagan (Bagan) by April 1544.

In the following dry season, a small Ava army raids down to Salin but is destroyed by larger Toungoo forces.

The successive defeats bring the long-simmering disagreements between Ava and Mohnyin of the Confederation to the forefront.

Faced with a serious Mohnyin-backed rebellion, Ava in 1545 seeks and agrees to a peace treaty with Toungoo in which Ava formally cedes all of Central Burma between Pagan and Prome.

Ava wll be beset by the rebellion for the next six years while an emboldened Toungoo will turn its attention to conquering Arakan in 1545–47, and Siam in 1547–49.