Objectives: Ambient air pollution (AAP) is an important risk factor for increased mental health morbidity. Studies have highlighted the effect of AAP on psychological stress and anxiety disorder.However, existing evidence regarding this is largely equivocal. This systematic review with meta-analysis aims to synthesize published evidence to calculate the pooled estimate of the effect of AAP on psychological stress and anxiety disorder. Content: A systematic bibliographic search was undertaken using PubMed, JGateplus, Google Scholar, and Cochrane Library for observational human studies published in English till 31st March 2020 reporting the effect of AAP on psychological stress and anxiety disorder. Study quality was assessed using the Joanna Briggs Institute critical appraisal tools. Meta-analysis was performed adopting a random-effects model using Meta-XL. Of 412 articles retrieved, a total of 30 articles [AAP and anxiety disorders, (n=17, 57%); AAP and psychological stress, (n=9, 30%) and AAP and both psychological stress and anxiety disorders, (n=4, 13%)] fulfilled the inclusion criteria covering a total population of 973,725 individuals. The pooled estimate (OR) of the effects of PM10 on psychological stress was 1.03 [(95% CI: 1.00, 1.05) (p=0.17,I 2=41%)]. The pooled estimate of the effects of NO2 and PM10 on anxiety disorder was 0.93 [(95% CI: 0.89, 0.97)(p=0.91, I 2=0%)] and 0.88 [(95% CI: 0.78, 0.98) (p=0.01,I 2=59%)] respectively. The pooled estimate of the effects of PM2.5 on anxiety Disorder was 0.88 [(95% CI: 0.72, 1.06)(p=0.00, I 2=80%)]. Summary and Outlook: The present study provides themost updated pooled estimate of the effect of AAP on psychological stress and anxiety disorder. Future studies should focus on longitudinal studies conducted in LIC and LMIC countries using uniform and standardized criteria for exposure and outcome assessment as well as robust adjustment for confounders to minimize methodological heterogeneity resulting in reliable and comparable estimation of environmental mental health burden.