A method of forming a package structure includes the following processes. A die is attached to a polymer layer. An encapsulant is formed over the polymer layer to encapsulate sidewalls of the die. A RDL structure is formed on the encapsulant and the die. A conductive terminal is electrically connected to the die through the RDL structure. A light transmitting film is formed on the polymer layer. An alignment process is performed, and the alignment process uses an optical equipment to see through the light transmitting film to capture the alignment information included in the polymer layer. A singulating process is performed to singulate the package structure according to the alignment information.