The Portlethen Moss  is an acidic bog nature reserve located to the west of the town of Portlethen, Aberdeenshire in Scotland. Like other mosses, this wetland area supports a variety of plant and animal species, even though it has been subject to certain development and agricultural degradation pressures. For example, the Great Crested Newt was found here prior to the expansion of the town of Portlethen. Many acid loving vegetative species occur in Portlethen Moss, and the habitat is monitored by the Scottish Wildlife Trust.
Portlethen Moss is the location of considerable prehistoric, Middle Ages and seventeenth century history, largely due to a ridge near the bog which was the route of early travellers. By at least the Middle Ages this trackway was more formally constructed with raised stonework and called the Causey Mounth. Without this drovers' road, travel through the Portlethen Moss and several nearby bogs would have been impossible between Aberdeen and coastal points to the south.