Purpose: This study analyzed the effect size of lavender essential oil and lavender blended essential oils on adult psychological factors. A meta-analysis was conducted to recommend an effective application strategy for improving psychological factors in adults.Methods: To analyze the effect size of lavender essential oil and lavender blended essential oils on psychological factors in adults, studies published over the last 10 years (January 2013 to December 2023) were collected. Studies were selected based on the population, intervention, comparison, outcomes, and study-format focusing on those that compared the pre and post psychological health of experimental group and control group and presented the mean and standard deviation. Data were analyzed using the version 4 software by Biostat (Englewood, USA).Results: Treatment with lavender essential oil alone showed highly positive effect on anxiety (0.731) and stress (0.730), followed by positive effects on sleep quality (0.673) and fatigue (0.601). Furthermore, treatment with lavender blended essential oils showed the most positive effects on sleep quality (1.383), followed by fatigue (1.159), stress (0.789), and anxiety (0.638).Conclusion: This study, discovered that lavender essential is effective in relieving anxiety and stress when used to improve adult psychological factors (anxiety, sleep quality, stress, and fatigue), and lavender blended essential oils are particularly effective in improving sleep quality and reducing fatigue. These results are expected to be valuable in prescribing treatments for individuals of various ages and lifestyles suffering from various psychological factors.