OBJECTIVE This study evaluated the evidence-based knowledge and emotional experiences of undergraduate nursing students regarding endotracheal suctioning. METHODS A cross-sectional, descriptive, survey design was used. Nursing students' knowledge level was measured using the Suctioning Knowledge Questionnaire, and emotions were assessed using the Clinical Stress Questionnaire. METHODS University undergraduate nursing programme. RESULTS The study included 445 undergraduate nurses. Students' mean knowledge score was 36.86 ± 14.45, and 85.8% of the total knowledge scores were 50 or less indicating a low level of knowledge. The mean score of the students who had experienced the suctioning procedure (44.5%, n = 198) was statistically higher than that of the students without experience (38.78 ± 12.62 and 35.32 ± 15.62, respectively) (p < 0.05). Students who performed the suctioning procedure expressed their emotions relating to suctioning as follows: I felt nervous (79.3%), worried (77.8%), frightened (70.2%), daunted (53.0%) and disgusted (51.0%). CONCLUSIONS The majority of nursing students' knowledge levels were insufficient. That they felt frightened or disgusted performing the procedure was noteworthy. Students should be given the opportunity to perform endotracheal suctioning and express their feelings about the procedure.