Commercial female sex workers (CFSWs) regularly or occasionally trade sex for money. Sex work is widespread, mainly in urban areas of Ethiopia. The study on the nutritional status of CFSWs is unavailable in Ethiopia, and data are also scanty at the global level. This study aims to assess nutritional status and associated factors among CFSWs in Hawassa city, Ethiopia. This cross-sectional study used facility-based mixed data collection methods (qualitative and quantitative). The study was conducted in three key population clinics in Hawassa city. A total of 297 CFSWs were randomly selected for the 'quantitative survey,' and twelve (n=12) purposively selected participants were involved in the 'qualitative study.' Body mass index/BMI (Kg/m2) was used in assessing the nutritional status of CFSWs. Statistical software packages were used for analyzing both quantitative and qualitative data. Significant variables (P<0.05) in bivariate analysis (Chi-square test) were incorporated in the multivariable analyses. Multinomial logistic regression (MNLR) was employed where dependable variable like 'normal BMI' (18.5-24.9 kg/m2) was set as a reference category and simultaneously compared with 'underweight' (<18.5 BMI) and 'overweight/obesity' (≥ 25 BMI) categories. Thus, two models, namely the underweight model (model-1: Underweight versus normal BMI) and the overweight/obesity model (model-2: overweight/obesity versus normal), were generated. The prevalence of underweight and overweight/obesity among CFSWs in Hawassa city were respectively 14.1% and 16.8%. Living alone (Adjusted odds ratio/AOR = 0.18), chewed Khat regularly (AOR = 0.23), used drugs regularly (AOR = 10.57), used drugs in exchange of sex (AOR = 4.97), and HIV positive status (AOR = 21.64) were significantly (P<0.05) associated with underweight (model-1). In the overweight/obesity model-2, having jobs other than sex work (AOR = 0.11), higher daily mean income (AOR = 3.02), being hotel/home-based CFSWs (AOR = 12.35), and presence of any chronic illness (AOR = 5.15) were significant (P<0.05) predictors of overweight/obesity. From the 'qualitative part' of this study, it was also revealed that 'lack of food and money' was the main influencing factor among CFSWs to enter into the sex business. Commercial female sex workers in this study faced a double burden of malnutrition. Multiple factors influenced their nutritional status. Substance abuse and HIV-positivity are the most significant predictors of being underweight and having higher income, being hotel/home-based CFSWs, and suffering from any chronic illness are associated with overweight/obesity. Government and other partners should be essential in providing comprehensive programs focusing on sexual, reproductive health, and nutrition education. Steps should be taken to improve their socioeconomic status and strengthen those good initiatives at key population clinics and other health facilities.