Cross arm of the transmission tower supports the transmission conductor. This paper is a review of previous studies on Glass-Fiber Reinforced Polymer (GFRP) cross arm and properties of fibreglass as an outdoor application. Based on the previous study, this paper reveals the durability and degradation of GFRP as performance cross arm in transmission tower. It was discovered that the behaviour of mechanical strength decreases while the GFRP are exposed to the outdoor environment, thus in general GFRP structures are capable to withstand into extreme/cyclic environment conditions. In addition, the GFRPs alone has others beneficial which generally more resilient compared to other conventional materials on strength which regard to high strength and stiffness-to-weight ratio, corrosion resistance, chemical stability, and the capability to be sustain in harsh environment and possible to longer the serviceability and perform as a good insulator in lightning impulse strength. It can be concluded that fibreglass cross arm has significant properties as a replacement for traditional conventional timber cross arm due to its durability in moisture effect.