Syrian state television broadcast what it said was a live ceremony from the presidential palace in Damascus during which Mr Assad took the oath of office.
A band played the Syrian national anthem after which Mr Assad was seen walking a red carpet past an honour guard into a hall packed with members of parliament and Christian and Muslim clergy.
Wearing a dark-blue suit and a blue shirt and tie, Mr Assad placed his hand on the Koran and pledged to honour the country's constitution.
He then launched into a speech in which he praised the Syrian people for holding the vote and for "defeating the dirty war" launched on them.
Throughout the three-year-old conflict, Mr Assad has maintained the conflict that has torn his nation apart was a western-backed conspiracy executed by "terrorists" - and not a popular revolt by people inspired by the Arab Spring uprisings, seeking democracy and disenchanted with his authoritarian rule.
As the conflict slid into civil war, Mr Assad repeatedly refused to step down and last month he was re-elected in a landslide victory in a vote dismissed by the opposition.