Background: Unmet supportive care need leads cancer patients to ineffective coping, worsened emotional distress, and a reduced quality of life. Little is known about unmet supportive care need in Ethiopia particularly in this study area. Objective: To determine the prevalence of unmet supportive care needs and associated factors among cancer patients admitted in oncology unit at Hawassa University Comprehensive Specialized Hospital, oncology center, Hawassa, Sidama, Ethiopia, 2022. Methods: A cross-sectional study design was conducted among 321 cancer patients from June 20 to August 5 2022, at Hawassa comprehensive specialized Hospital oncology center. Simple random sampling technique was used to recruit the study participants. The data were collected using a structured questionnaire through face-to-face interview. Data was entered into Epi-Data version 4.6 and was exported to SPSS version 26 for analysis. Multivariate logistic regression was used to describe association between dependent and independent variables. p-value of less than 0.05 was considered statistically significant. Result: Out of 321 sampled population 311 were responded to this study. The mean age of the respondents was 45.16±14.27. Unmet supportive care needs were highest for the health system and information need domain (72.3%) followed by psychological (71.1%), physical and daily living (47.3%), patient care/ support (43.4%) and sexuality (27.7%). Low income (AOR = 5.96; 95% CI: 2.29–14.13) and middle income (AOR = 4.64; 95% CI: 1.48–14.50) were significantly associated with unmet health system needs. Rural residence (AOR = 2.73; 95% CI: 1.27-5.83) and late-stage cancer (AOR = 2.95; 95% CI: 1.02-8.52) were significantly associated with unmet physical domain. Co-existing illness was associated with unmet physical (AOR = 2.73; 95% CI: 1.27–5.83), psychological (AOR = 2.71; 95% CI: 1.16–6.33), and patient care (AOR = 1.87; 95% CI: 1.09–3.52), respectively. Time since diagnosis had a statistically significant association with the sexuality needs (AOR = 1.05; 95% CI: 1.01-1.11). Conclusion and recommendation: This study revealed the highest prevalence of unmet supportive needs of cancer patients in Health system and psychological need domains. Income, Residence, late-stage cancer, time since diagnosis and co-existing illness were associated across one or more unmet supportive care needs. Hence, the supportive care of cancer patients should be incorporate into the cancer treatment protocol based on the specific predictors identified.