Bolts are widely used in slope engineering, tunnel and large cave supporting structures, as well as restoration of engineering structures. They can improve the strength and stability of ground, rock mass, and other structures. The traditional steel bolt has some disadvantages, such as easy corrosion, heavy weight, and difficult operation. Glass Fiber Reinforced Polymer (GFRP) is more resistant to chloride, stronger and lighter than steel. Those advantages make it a better alternative in some fields of engineering. To utilize GFRP bars as rock bolt, some aspects of its behavior, such as bond strength in mortar, bearing capacity, and bond stress distributing along its interface, have to be examined. This paper presents a research on bond behavior of GFRP rock bolts. A concrete block is used to represent rock mass in laboratory. Modified pull out tests were conducted on selected GFRP bars and compared with steel ones that were grouted with mortar in concrete blocks. Bond characteristics of mortar grouted GFRP rock bolts with diameter 16mm were mainly evaluated and other specs of bolts were also discussed.