Imperial Oil is closing its refinery in Dartmouth and converting it into a marine terminal.
The company said it could not find a buyer for its facility near Woodside to continue operating as a refinery.
Vice-president Gilles Courtemanche told reporters there is too much oil on the market and the facility is too small.
It will refine its last barrel later this year.
Imperial Oil said it will do all it can to protect the environment while it takes apart the facility.
About 400 people have work ties to the refinery, which has operated for the past 95 years. About 80 employees will either retire or stay on. The company said the rest will be offered work elsewhere in Canada.
The refinery produces most of the gasoline sold in Nova Scotia.