Abstract Purpose As the number of cancer survivors increases, addressing their unmet supportive care needs (USCNs) has become crucial. This study aimed to evaluate the influence of financial toxicity on USCNs and identify comprehensive factors associated with USCNs among adults’ cancer survivors. Methods A cross-sectional survey using convenience sampling from the 2022 Korean Population Census. Data were collected online between November 17 and December 15, 2022. The study included 1,038 cancer survivors aged 19 years or older who had completed primary treatment. Multivariable logistic regression was analyzed to identify factors associated with USCNs. Results Two-thirds (65.7%) of cancer survivors experienced severe financial toxicity, correlating with high unmet supportive care needs. Among those who reported a severe financial burden, a substantial 170 out of 187 respondents, or approximately 90.9%, were identified as having high unmet supportive care needs. Cancer survivors had the highest needs in the order of ‘management of psychological symptoms’ and ‘coping and emotional needs’. Cancer survivors diagnosed between 5 and 10 years ago were found to be less likely to report unmet supportive care needs compared to those diagnosed more recently, with an odds ratio of 0.14. Additionally, breast cancer survivors and individuals who were unemployed at the time of diagnosis had a higher likelihood of experiencing unmet supportive care needs, with adjusted odds ratios of 1.68 (95% confidence interval: 1.088-2.603) and 1.80 (95% CI: 1.125-2.891), respectively. Conclusions Cancer survivors with moderate to severe financial distress were more likely to be at risk of experiencing a high level of unmet supportive care needs. Coping and emotional needs are the most important concerns among the unmet needs of cancer survivors regardless of the time since cancer diagnosis. Key messages • Cancer survivors in South Korea with moderate to severe financial distress are twice as likely to face a high level of unmet supportive care needs. • The most significant unmet supportive care needs among South Korean cancer survivors relate to coping and emotional support, highlighting the need for enhanced mental health services.