Hepatitis B virus (HBV) co-infection with HIV is becoming a major challenge due to shared routes of transmission. Therefore, screening HBV in HIV infected individuals should be a routine clinical practice. In Ethiopia practice of routine HBV screening, Use of HAART regimens with dual Anti-HIV/HBV action & their effect on HBSAg sero reactivity is not well studied. To determine the sero prevalence of HBSAg in HIV infected patients, Pattern of HAART use in Co infected patients and Effect of HAART on HBSAg serore activity. A Six years Retrospective review of HIV infected patients for whom HBSAg testing was done previously was taken by reviewing the medical records of 424 patients following in ART clinic of Ayder referral hospital from January 1,2009 – January 15, 2016. The prevalence of HBV in HIV infected patients is found to be 10%. Among co infected patients 81.8% of patients were put on HAART regimens with two agents active against HIV & HBV which is in line with international guidelines. HBSAg Sero Conversion rate was found to be 63.6% in co infected patients who took HAART for more than one year. HIV/HBV Co infection rate in Ayder hospital is comparable with the previously done studies & Practice of HAART use in ARH is in accordance with International HIV & HBV treatment guidelines recommendations. All of the seroconverted patients were taking Tenofovir, Lamivudine, Efavirenz regimen proving the importance of this regimen on co infected patients.