Background Needle insertion into an implantable central venous port catheter may lead to procedural pain and anxiety in cancer patients. Objective The aim of this study was to determine the effects of inhalation aromatherapy on procedural pain and anxiety after needle insertion into an implantable central venous port catheter. Methods This study included 123 cancer patients who were scheduled to undergo chemotherapy. Patients were randomly assigned to either the lavender group (n = 41), the eucalyptus group (n = 41), or a control group (n = 41). Participants in the intervention groups inhaled 3 drops of essential oil for 3 minutes before needle insertion into an implantable venous port catheter. Patients in the control group received no intervention before needle insertion. Data were collected using the visual analog scale (VAS) and State Anxiety Inventory. Results The average VAS scores of the lavender group were significantly lower than those of the control group (P < .05). There were no significant differences in the average VAS scores between the eucalyptus group and the control group (P > .05). In addition, the average State Anxiety Inventory scores of the lavender group, the eucalyptus group, and the control group were not significantly different (P > .05). Conclusion Inhalation aromatherapy with lavender may be an effective technique to relieve pain related to needle insertion into an implantable central venous port catheter. Implications for Practice Inhalation aromatherapy with lavender oil may be useful in the management of procedural pain levels during needle procedure. However, further randomized controlled trials are needed to validate this study.