In this paper, the stress concentration factors (SCFs) in tubular T/Y-joints reinforced with fiber reinforced polymer (FRP) are investigated. A total of 134 3-D FE models was generated and analyzed under compressive load. The effect of FRP layers and joint geometry on the SCFs and the SCF ratio of the reinforced to the unreinforced joints were investigated through a parametric study. Results showed that the SCF of an FRP reinforced T/Y-joint can be down to 34% of the SCF of the corresponding unreinforced joint. Also, two parametric formulas were proposed for determining the SCFs in T/Y-joints reinforced with FRP.