Abstract Objective Evidence on the impact of shared decision-making (SDM) on the financial toxicity (FT) of patients with cancer in real clinical settings is lacking. Using a nationwide patient survey in China, we aimed to identify the prevalence of SDM, FT as well as its consequent coping actions, and investigate their associations in adult patients with cancer. Methods A cross-sectional survey was administered to patients with cancer near discharge at 33 tertiary public cancer hospitals across China between January and March 2021. The FT was measured using the COST (comprehensive score for financial toxicity) tool and was categorized into 3 groups: no (COST 26-44), mild (COST 14-25), and moderate or severe (COST 0-13) FT. SDM was measured using 2 items from patient’s perspective. The surveyed questionnaire also included patient’s coping actions, demographics, and clinical information. Multinomial logistic regression was used to investigate the association between SDM and FT, and for sensitivity analysis, linear regression was also used taking the COST score as a dependent variable. Pearson’s chi-square tests were used for association analyses of coping actions with FT and SDM. Results A total of 5008 adult patients with cancer were included, of which 26.18%, 54.13%, and 19.69% patients were categorized as no FT, mild FT, and moderate or severe FT with the average COST score of 21.0 for all patients. Besides, 3943 (78.73%) patients reported a better SDM. Better SDM had significantly lower odds of developing high FT than worse SDM (adjusted ORmild vs no 0.50, 95% CI 0.39-0.56; adjusted ORmoderate or severe vs no 0.63, 95% CI 0.50-0.80). In sensitivity analysis, better SDM was significantly associated with higher COST scores (β: 1.34, 95% CI 0.85-1.83), which indicated lower FT. Patients with higher FT were more likely to take adverse coping actions including treatment nonadherence, limiting basic health service expense, reducing leisure activity expense, and loan. Conclusions Adult patients with cancer reporting worse SDM tended to experience higher FT and those with higher FT tended to take adverse coping actions. Understanding the impact of SDM on FT is crucial to inform early interventions designed to mitigate FT and consequent coping actions in cancer care practice.