The 2.4 kilometres stretch of Wallgrove Road between Chandos Road and The Horsley Drive has been reduced to 70 km/h.
The previous 80 km/h speed limit between Horsley Park and Cecil Hills was changed on Monday in response to requests from residents and motorists.
The Roads and Maritime Services said the speed limit change will provide improved safety for motorists and pedestrians as well as provide a more consistent journey.
Work was carried out to install new speed limit signs on Monday and the new speed limit will take effect once the signs are in place. Motorists are reminded to drive to sign posted speed limits at all times for the safety of all road users.
Residents can sign up at the Safer Roads NSW website to receive updates about changes to permanent speed limits in their area.