In this study, to investigate frictional behavior and maximum strength of GFRP members connected by high strength bolts and splice plates made of stainless or GFRP plates, slip test and bolt relaxation test are carried out. And FE analysis is executed to study on mechanism of stress concentration. From the slip test, slip coefficient of the specimen with stainless splice plates is lager than 0.4 and it is found that the slip coefficient can calculate by toribology theory. From the FE analysis, the maximum strength of the GFRP firictional bolted joint can estimate based on consideration of stress concentration. Relaxation test for one year provides the amount of decrements of the bolt axial forces of each connection.