Previous studies have suggested a significant association between diet quality and mental health. However, a limited number of studies have utilized the Prime Diet Quality Score (PDQS) to examine this association. Additionally, no study has yet compared the PDQS and Healthy Eating Index-2015 (HEI-2015) in terms of their association with depression and anxiety.This cross-sectional study aimed to investigate the association between diet quality, measured by the PDQS and HEI-2015, and the odds of depression and anxiety in adults.This study utilized data from the LIPOKAP study, which was conducted between February 2018 and July 2019 in five cities in Iran. We included 1994 adults aged 18 and above who were selected through a multistage cluster sampling method. Participants completed a validated semiquantitative food frequency questionnaire (FFQ) to evaluate their dietary intake. The FFQ was used to calculate the PDQS and HEI-2015. Depression and anxiety levels were determined using the Hospital Anxiety and Depression Scale (HADS).The participants had a mean age of 39.79 ± 13.87 years, with females accounting for 1,041 (52.2%) of the total population. PDQS showed a significant inverse association with the odds of depression (OR = 0.45, 95% CI: 0.28-0.71) and anxiety (OR = 0.40, 95% CI: 0.25-0.62) in the fully adjusted model. Similarly, the highest quartile of HEI-2015 showed a significantly lower odds of depression (OR = 0.60, 95% CI: 0.40-0.90) and anxiety (OR = 0.62, 95% CI: 0.42-0.92) compared to the lowest quartile.Both PDQS and HEI-2015 were associated with a reduced risk of depression and anxiety. However, the PDQS demonstrated a stronger inverse association with these risks compared to the HEI-2015. This suggests that the PDQS could be a more beneficial dietary pattern for preventing depression and anxiety compared to HEI-2015. Further large-scale studies are required to confirm these findings.