Objective To study the LDH and GDH of the swordtail inbred strain RR-B with isoenzyme electrophoresis and analyze genetic purity of strain RR-B. Methods Using polyacrylamide gel electrophoresis, two isozymes(LDH and GDH) of swordtail fish were studied; the LDH of eye and GDH of liver were analysed in both unbreeding and RR-B strain swordtail fish. Results Swordtail fish RR-B strain has same zymogram of LDH and GDH,while the isozyme patterns of swordtail fish are polymorphic. Conclusion The inbred strain of swordtail fish has reached a high degree of genetic purity.