This study compared outcomes, including pain, fatigue, anxiety, satisfaction, health-related quality of life (HRQOL), ease of access, and unexpected emergency room (ER) visits, for patients with cancer in South Korea who were cared for by an oncology clinical nurse specialist (CNS) with patients with cancer who were not. Self-report questionnaires and semistructured interviews were used to appraise the performance of oncology CNSs, and medical characteristics were obtained through chart review. CNS interventions were found to diminish some intensity scores of pain and fatigue, and to increase HRQOL, satisfaction with trustworthiness, and ease of access. No significant effects were observed on anxiety or unexpected ER visits. The current study provides evidence that oncology CNSs are effective in South Korea, which will be the basis of validating the implementation and expansion of policy for oncology nursing.