Bloomberg won the election by 51 per cent of vote defeating Democratic challenger William Thompson.
Bloomberg, a former Republican who ran as an independent candidate, spent more than $100 million of his own money on the campaign.
Bloomberg is the richest man in New York. He has been a popular manager of New York's economy and was credited with reducing crime for the last eight years.
He was first elected mayor in the wake of the Sep 11, 2001, terrorist attacks and inflicted tens of billions of dollars in damage to the city's infrastructure, Wall Street firms and jobs.