Background <p>Nutritional impacts of tuberculosis (TB) have long been recognised. According to the national TB treatment guidelines, individuals with TB are assessed for under-nutrition during treatment initiation and receive regular nutritional counselling and support, including food supplementation, when the condition is detected. However, the extent of under-nutrition after completing intensive-phase of treatment, which may indicate its potential persistence, remains unclear especially in resource-limited settings.</p> Objective <p>This study aimed to assess the extent of under-nutrition and associated factors among adult TB patients completing intensive-phase treatment at public health facilities of Kembata Zone, Central Ethiopia Region.</p> Methods <p>We conducted a cross sectional facility-based study among 334 adult TB patients in the continuous-phase treatment. Participants were recruited using a cluster sampling technique. Bivariate logistic regression analysis was performed to assess the association between under-nutrition and explanatory variables. Odds ratios along with 95% confidence interval (CI) were estimated to identify factors significantly associated with under-nutrition using multivariable logistic regression analysis. The level of statistical significance was determined at P-value less than 0.05.</p> Results <p>Under-nutrition was detected in almost 19% of participants. Sociodemographic and clinical factors contributed to the presence of under-nutrition in the continuous-phase of treatment. Not attending formal education (AOR: 4.2; 95%CI: 1.7–10.4) and living in a family of more than five (AOR: 2.3; 95%CI: 1.2–4.6) were sociodemogrphic factors associated with the occurrence of under-nutrition. Having extra-pulmonary TB (EPTB) (AOR: 3.2; 95%CI: 1.4–7.6) and shorter length (less than four months) of treatment (AOR: 4.3; 95%CI: 1.9–9.5) were clinical conditions linked with under-nutrition.</p> Conclusions <p>Our study identified a higher prevalence of under-nutrition in the continuous-phase of TB treatment than the targets of clinical guidelines, which expect optimal nutritional status in all patients. This may suggest potential persistence of poor nutritional status (or a lack of weight gain) from the earlier period of treatment. This may reflect lower understandings of the nutritional impact of TB in association with a lack of formal education, and a limited adequate diet due to a larger family size. Being in the earlier period of continuous-phase treatment and having EPTB also increased the likelihood of under-nutrition. Continuous monitoring and support is suggested throughout the treatment course with a particular focus on individuals with a lower socioeconomic background and EPTB.</p>