In this study, 300 dairy cattle imported from Australia were investigated  for diagnosis of bovine leukosis through detection of bovine leukemia virus (BLV)  antibodies, BL viral nucleic acid and antigen of BLV (which causes this disease) by performing, enzyme linked immunosorbent assay (ELISA) to serum samples, polymerase chain reaction (PCR) to blood samples and immunohistochemical stainig technique using avidine biotin peroxidase complex (ABC) method to lymph node biopsies respectively. 200 of these dairy cattle were investigated immediately After arrival to Islamic Jeddah Port, Kingdom of Saudi Arabia (KSA) during the obligatory quarantine period (21 days) by performing the three previously mentioned techniques one time. While, the remaining 100 dairy cattle were selected from one dairy farm imported these cattle from Australia also one year before beginning of the study and investigated by these techniques 3 successive times one month apart, in addition to investigate one pooled bulk tank milk sample by ELISA. 50 out of these 100 cattle were selected randomly and 50 selected from low producing cattle in the farm. Concerning to recently imported dairy cattle in port `s quarantine, BLV antibodies were detected in 16 cattle, BL viral nucleic acid was detected in 21cattle and BL viral antigen was detected in 24 cattle after performing ELISA, PCR and ABC respectively. After performing first investigation tom cattle of dairy farm, BLV antibodies were identified in 6 cattle (5 of them from low milk producer cattle), BL viral nucleic acid was detected in 7 cattle (6 of them from low milk producer cattle) and BL viral antigen in 9 cattle (8 of them from low milk producer cattle). In the second investigation of cattle of the dairy farm, no change in results of ELISA was observed while number of positive cases increased to 9 and 11 with PCR and ABC respectively. The third investigation of dairy farm cattle revealed seroconversion of 2 cattle that were negative with first and second ELISA while no change of PCR and ABC results were recorded. Pooled bulk tank milk sample was positive to BLV antibodies with 3 successive ELISA. Results of this work showed that not few numbers of imported dairy cattle were infected with bovine leukosis which seemed to has a correlation with low milk production. All infected cattle were apparently healthy, therefore, laboratory investigation of imported dairy cattle for BLV before introducing of these animals is very important. This study proved that ABC method is more sensitive than PCR and ELISA and PCR is more sensitive than ELISA, at the same time ABC and PCR could detect new infections before ELISA. All results of this study cleared the importance of performing ELISA and PCR to investigate all imported dairy cattle before permission of leaving quarantine. To control this disease, all dairy farms (specially those of low milk production without obvious cause) should be investigated by performing ELISA to pooled bulk tank milk sample, if it gave positive result, all farm animals should be examined using PCR and ELISA followed by eradication of positive animals. In spite of high sensitivity of ABC technique, it is not recommended to be used now as its steps still complicated and expensive but with continuous work to simplify its steps and decrease its cost, may be it will the ideal technique of diagnosis of this disease in the future.