In this paper, an experimental study has been conducted on strengthening of reinforced concrete (RC) connections by FRP sheets. The innovation of this research is using narrow grooves on critical regions of connection to increase the adherence of FRP sheets and prevent their early debonding. Therefore, four RC connections were made and tested under a constant axial load on the column and an increasing cyclic load on the beam. The first specimen, as the standard reference specimen, had close tie spacing in ductile regions of beam, column and panel zone based on seismic design provisions, and the second specimen, as the weak reference specimen did not have these conditions in all regions. Two other weak specimens were strengthened using two different strengthening patterns with FRP sheets one by ordinary surface preparation and the other with surface grooving method for installing FRP sheets on the connection. The results showed that ultimate load and ductility of the weak specimen compared to standard specimen decreased 25% and 17%, respectively. The shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened specimens. Also, it was observed that early debonding of FRP sheets was prevented in the strengthened connection with grooving pattern and so had desirable ductility and bearing capacity similar to the standard specimen.