Background: Tuberculosis is a contagious air born disease caused by Mycobacterium tuberculosis species and the leading causes of morbidity and mortality among people living with HIV/AIDS worldwide. Globally, it causes ill-health among millions of people living with HIV/AIDS each year. Objective: To identify determinants of Tuberculosis among HIV infected adults in public health facilities, in Horro Guduru Wollega Zone, 2019. Methods: Unmatched case-control study was conducted among 127 cases and 255 controls which were selected using systematic random sampling technique. Data were collected by record review and through face to face interview. Then, analysis was done using SPSS version 25.To identify determinants of tuberculosis multivariable logistic regression was employed. Adjusted odds ratio was calculated with 95 % CI to show strength of association and P-value < 0.05 was used to declare statistical significance.Results: - A total of 127 cases and 255 controls were participated into the study with 97.2% response rate. Aged ≥35 years [ AOR= 2.63, 95% CI(1.29,5.36)], alcohol consumption [AOR=3.34,95%CI(1.68,6.99)], Having CD4 cells <200 [AOR=3.67, 95% CI (1.5, 9.1)], Having Haemoglobin <11g/dl [AOR=3.77, 95%CI(1.84,7.72)], Imprisoned in the past 2 years [AOR=4.22, 95%CI(1.56, 11.37)], Living with TB patients in the same house [AOR=14.97, 95% CI(1.99, 21.63)] were factors associated with TB among HIV infected adults. Importantly, using Cotrimoxazole prophylaxis [AOR=0.193, 95% CI(0.81,0.46)] had a protective effect from acquiring TB. Conclusion and Recommendation: Being in old age, alcohol use, Chewing khat, Having CD4cells <200, Advanced WHO clinical stage, Hgb <11g/dl, Imprisoned in the past 2 years, History of previous TB and living with TB patients in the same house were factors associated with TB/HIV co-infection. Using Cotrimoxazole had a protective effect from acquiring TB/HIV co-infection. For most of these determinants interventions can be made at individual and institutional levels, whereas, some factors need societal level integrations.