Ofloxacin (Hoe-280) (20 mg/kg), norfloxacin (40 mg/kg), pefloxacin mesylate dihydrate (40 mg/kg)and ciprofloxacin (50 mg/kg) are administered by gavage twice daily for three consecutive weeks. 6 weeks after treatment, the test animals are euthanised and Achilles tendon specimens are collected. A computer monitored tensile testing machine was utilised for biomechanical testing. The mean elastic modulus of the control group was significantly higher than that of the norfloxacin and pefloxacin groups (p<0.05 and p<0.01, respectively). The mean yield force (YF) of the control group was significantly higher than those of ciprofloxacin, norfloxacin and pefloxacin groups (p<0.001, p<0.05 and p<0.01, respectively). The mean ultimate tensile force (UTF) of the control group was significantly higher than of the ciprofloxacin, norfloxacin, and pefloxacin groups (p<0.001, p<0.05 and p<0.01, respectively). Hyaline degeneration and fibre disarrangement were observed in the tendons of the ciprofloxacin, pefloxacin, and ofloxacin treated-groups, whereas myxomatous degeneration was observed only in the ciprofloxacin and pefloxacin groups.