Objectives: This study aimed to investigate the effect of Time Perspective Therapy (TPT) on dark tetrad personality traits of mothers and Separation Anxiety Disorder (SAD) of their preschool children. Methods: This is quasi-experimental clinical trial with pre-test, post-test, follow-up design. Participants were the mothers of 32 preschool children with SAD in Kazerun County, Iran in winter 2019 who were selected using a convenience sampling method and randomly assigned into intervention (n=16) and control (n=16) groups. Mothers in the intervention group received TPT at six 90-min sessions, once per week. The data were collected using the Dark Triad Dirty Dozen inventory, Short Sadistic Impulse Scale, and Children Symptom Inventory. The collected data were analyzed using repeated measures ANOVA in SPSS v. 22 software. Results: The TPT led to a significant decrease in SAD symptoms and narcissism (P≤0.05) at the post-test and follow-up phases, but had no any significant effect on other dark tetrad personality traits of mothers (P≥0.05). Conclusion: The TPT of mothers decreases their narcissism and the SAD symptoms of their children.