The China - Britain boundary markers, including the land, customs and maritime boundary markers, is the historical witness of the British colonial invasion and plunder. The land boundary mark in Chung Ying Street is the relic of most historical value dating from when Britain established the boundary at the north end of the New Territories . As a result of aging, as well as natural and human factor, the Chung Ying Street boundary marker has suffered varying degrees of damage. This research investigates and analyses the regional distribution, weathering, biological decay, surface pollution and color change, and mechanical damage to the boundary markers. The specific types of the damage and the causes of it were analyzed. Considering the current condition of the makers, we suggest a series of scientific methods for protection, including washing, surface protection, waterproofing and environmental remediation. In this way the boundary markers could be preserved and their use for educational purposes extended. The methods described would also be valuable for the protection of the customs and maritime boundary markers.