Provided are a package structure and a method of forming the same. The package structure includes a package substrate, a first die, and a stiffener ring. The first die is disposed on the package substrate and has a first sidewall and a second sidewall opposite to each other. The stiffener ring is disposed on the package substrate to surround the first die. The stiffener ring has an inner sidewall facing the first die, and the inner sidewall at least has a slant sidewall facing the first sidewall of the first die.