This study aims to investigate health behaviors and psychological burdens in adolescent children of cancer parents. We compared health behaviors and mental health outcomes between 266 adolescent children with a parent diagnosed with cancer and 3163 control adolescents aged 12–19 years using data from the Korean National Health and Nutrition Examination Survey (KNHANES) from 2010 to 2018. Alcohol use of adolescents increased between 2 and 5 years after parental cancer diagnosis (adjusted odds ratio [aOR], 1.72; 95% confidence interval [CI], 1.01–2.94) but decreased after 5 years. Parental cancer was associated with increased vaccination uptake in adolescents within 1 year of diagnosis (aOR, 3.19; 95% CI, 1.55–6.54), but after 2 years, there was no difference from rates in their peers. Maternal cancer was associated with increased depression among adolescents (aOR, 1.73; 95% CI, 1.10 − 2.73). Although the risks of suicidal thoughts/plans/attempts increased within 1 year after parental cancer diagnosis (aOR, 2.96; 95% CI, 1.00 − 8.83), it reduced 2 years after diagnosis, leading to no significant difference from the frequency in peers. Within five years after the parent was diagnosed with cancer, support for their adolescent children's health behaviors and mental health is necessary in the community.