Nursing surveillance is a defense mechanism that protects patients from adverse events, as it is a systematic process that contributes to nurses’ detection of and intervention in dangerous situations. This descriptive cross-sectional study examined the degree of nursing surveillance activity performed by clinical nurses, nurses’ perceived importance of nursing surveillance, and their perception of patient safety culture. The study aimed to identify the predictors of nursing surveillance activity. Participants included 205 clinical nurses from two secondary hospitals and two tertiary hospitals in Changwon-si and Cheongju-si, South Korea, who had at least one year of clinical experience. Nursing surveillance activity was high among nurses who were assigned fewer than 1.88 patients, who worked in a tertiary hospital, and those who scored 7.0 or higher in nurses’ perceived expertise. Nursing surveillance activity was significantly positively correlated with nurses’ perceived importance of nursing surveillance and patient safety culture. A hierarchical multiple regression analysis was performed to identify the predictors of nursing surveillance activity. Nurses’ perceived expertise, perceived importance of nursing surveillance, patient safety culture, and type of hospital explained 65.3% of the variance of nursing surveillance activity. This study is significant as it provides an assessment of the extent and key predictors of nursing surveillance activity.