Fiber Reinforced Polymer (FRP) external bonding system is a popular technique that is used to strengthen and repair existing structural elements due to its high strength to weight ratio, fatigue resistance, non-corrosiveness and ease of handling and application at the site. In this research, the focus is on the behavior of FRP external bonding system use to strengthen Reinforced Concrete (RC) beam and column when subjected to be exposed to out-door climate, submersion in tap water, sea-liked water and high concentration of sodium sulfate (Na2SO4) solution. This area of work has not yet fully explored in Cambodia. This research project is attempting to fulfill that gap. The scope of work for this research divided into 3 categories such as RC beam-column specimen strengthened externally by one layer of Glass Fiber Reinforced Polymer (GFRP) sheet that expose into different exposures with duration of 1000, 2000, and 3000 hours. The GFRP in the form of sheet roll was used as material to strengthen on tension face of RC beam in order to improve the flexural strength and wrapped around RC column in order to increase the compressive strength. The result, FRP external bonding system maintained its capacity after exposure to aggressive degradation agents in the scope of 1000 and 2000 hours. However, after being submerged for 3000 hours in tap water, strengthened RC column specimens started to decrease the ultimate load due to degradation on GFRP sheet. The most aggressive exposure condition was tap water during this scope period of work.