Part of College Road, between Haywards Heath and Ardingly, will be closed for five weeks from the beginning of July.
Southern Gas Networks will be working to upgrade the existing gas main within the road on the bridge that crosses the River Ouse.
The road, between its junction with Copyhold Lane and the Hanson Aggregates quarry, will be closed from July 6 - a finish date has not been provided.
The work is the final stage in a £400,000 investment project to replace a two-kilometre section of the old metal gas main in College Road with new plastic pipe.
This forms part of our ongoing mains replacement programme in the area to maintain the safety and reliability of the gas supply network.
A signed diversion route will be in place throughout the road closure and there will be temporary two-way traffic lights in place outside Ardingly College. Access for residents will be maintained at all times.
Steve King, planner for gas distribution company SGN, said: “I would like to apologise for any inconvenience that may be caused by this project. We have worked closely with West Sussex County Council in planning the work, which will be carried out during the school summer holidays to minimise disruption. We will continue to keep in close contact with them as the work progresses.
“We understand that roadworks can be very frustrating, but the new plastic pipe has a minimum life-span of 80 years. This means that once the work has been completed, people in Ardingly will be able to enjoy the benefits of a continued safe and secure gas supply for many years to come.”