Background: Food insecurity and HIV/AIDS are common problems in resource limited setting particularly Sub- Saharan countries. Both are intertwined and worsening one another in a vicious cycle through a mixture of various factors. However, the magnitude of food insecurity and its associated factors among People Living with HIV/AIDS are not well studied in Ethiopia. Objective: The aim of this study was to assess the prevalence of food insecurity and its associated factors among adult people living with HIV/AIDS receiving HAART. Methods: Institution based cross-sectional study was conducted. A total of 338 study subjects were enrolled in the study and systematic random sampling technique was used to select the study participants. Structured and pre-tested questionnaire was used to collect socio-demographic, clinical and nutrition related data. Both bivariate and multivariate logistic regression analyses were used to assess the effect of the various factors on food insecurity. P-value ≤ 0.05 at 95% CI was considered statistically significant. Results: The overall prevalence of food insecurity among PLWHA receiving HAART at Butajira hospital was 78.1% (95% CI: 73.7%-82.8%). Mild, moderate and severe food insecurity was observed on 4.4%, 32.0% and 41.7% participants respectively. Multivariate Logistic regression analysis revealed that living in rural area (AOR=1.94; 95% CI: 1.11, 3.38), low monthly income (AOR=7.80; 95% CI: 7.80 (3.55-17.1) and inadequate household dietary diversity (AOR=14.4; 95% CI: 4.90, 42.6) were significantly associated with food insecurity. Conclusion: Food insecurity is high among PLWHA receiving HAART at Butajira Hospital, Southern Ethiopia. Living in rural area, low monthly income, under-nutrition and inadequate household dietary diversity were the significant factors for food insecurity.