Alejandro Melchor (1900-1947) was a Filipino civil engineer, mathematician, educator, and member of the Cabinet of the Philippines. A native of Ibajay, Aklan, Melchor was also known for his work on pontoon bridges during the Second World War.
The historic Melchor Hall in the University of the Philippines Diliman campus is named after him. The hall houses most of the units of the UP College of Engineering. A building in the Philippine Military Academy was also named in his honor.
In 1924, Melchor graduated in civil engineering with the highest honors from the University of the Philippines. By then, the College of Engineering was barely fifteen years old and was still located in the Manila campus.
During the term of Edward R. Hyde as dean of the UP College of Engineering (from 1926 to 1940), Alejandro Melchor served as the College Secretary. Prior to this position, Melchor was a regular member of the engineering faculty. Considered a brilliant mathematician in his time, Melchor also became the head of the mathematics department of the Philippine Military Academy.
Melchor was known for designing the pontoon bridges used by the U.S. Army during the Second World War. According to , Melchor's work "contributed significantly in winning the war for the Allied Forces". Melchor also attained the rank of colonel.
Melchor obtained his highest rank of public service when he became the Secretary of National Defense in President Manuel L. Quezon's Cabinet. Upon Quezon's death and Sergio Osmeña's succession as president, Melchor became the Military Adviser of the war cabinet. This was during the Second World War, when the Philippine government was in exile.
He died in 1947.