Thermosetting copolyester adhesives were prepared by copolymerizing p-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA) and 4-functional crosslinkable oligomers. Two different crosslinkable oligomers having four carboxylic acid or four acetoxy end groups were evaluated. The transition from thermoplastic to thermosetting character occurred when 10 wt% oligomer was added to the 73/27 HBA/HNA copolyester. Tensile strength and lap shear strength of the copolyesters have been investigated by both tensile test and adhesive test using an aluminum sheet. In the case of tensile strength of a single fiber, the values for the copolyesters containing oligomer decreased to about 90% of the 73/27 HBA/HNA fiber in the high draw ratio region while a slight decrease in tensile strength was observed in the low draw ratio region. An adhesive test using aluminum sheet revealed a decrease in the lap shear strength up to 15$0^{circ}C$ for all copolyesters except the copolyester containing 10 wt% crosslinkable oligomer. Compared to 73/27 HBA/HNA copolyester, an improvement in the lap shear strength of the copolyesters containing 5 wt% oligomer was observed up to 15$0^{circ}C$. On the other hand, the copolyester containing 10 wt% crosslinkable oligomer displayed a small change in the lap shear strength with temperature.