Background Evidences from previous studies claim that informing children about their HIV status has long term positive implications in the HIV disease management, children's quality of life and ART drug adherence. However, in many parts of the Sub-Saharan African Countries, the HIV status disclosure among children reaches from 0 to 69.2%. Since the issue of disclosure is complex and highly influenced by socio-cultural characters and perception of the community towards HIV disease, it is important to investigate the up to date evidence which will help in designing contextualized approaches for disclosure. The objective of the current study was to assess the HIV status disclosure and its associated factors among children on ART in West Shoa Zone, Ethiopia.Methods Institutional based quantitative cross-sectional study supplemented by qualitative was conducted from February to April /2019 among 247 caregivers and or their children.Results The mean age of the children was 11.11±SD2.8, and 43.6%, (95% CI: 37, 50.9) of the children were fully disclosed. The average age at disclosure was 11 ±SD2.12. The main reasons for the disclosure were for drug adherence and better self-care, while underage was the commonest reason for nondisclosure. Compared to the age (10-15) years, the child in the age (6-9) was 97% [AOR: 0.027, 95% CI: 0.003, 0.22, P<0.001] less likely to be disclosed. Female children were 2.7 times more likely to be disclosed compared to males children [AOR: 2.73, 95% CI: 1.24, 6, P<0.013].Conclusion The current finding reveals that the HIV status disclosure is generally low, and the decision to disclose or not to do so is affected by many factors like child age, and child sex. This will affect directly or indirectly the child drug adherence, treatment outcome and also disease transmission.