Objective To investigate the expression level of plasma adiponectin（ APN） in patients with depressive disorders and its clinical significance. Methods From August 20， 2023 to May 19， 2024， 90 patients with first-episode depressive disorders attending the First Psychiatric Hospital of Harbin were selected as case group， and 90 healthy volunteers during the same period were selected as control group. General clinical data were collected and the 24-item Hamilton Depression Scale（ HAMD-24） was used to assess the severity of depressive disorder in case group. Plasma APN levels were measured by enzymelinked immunosorbent assay（ ELISA） in both groups of subjects. Spearman correlation was used to analyze the correlation between plasma APN levels and HAMD-24 scores and the duration of depressive disorders， and multifactorial Logistic regression was used to predict the factors affecting the occurrence of depressive disorders. The diagnostic value of plasma APN levels for depressive disorders was analyzed using the receiver operating characteristic（ ROC） curve. Results Plasma APN levels were 50.47（ 48.86，52.16） ng/mL in case group and 55.82（ 52.78， 56.00） ng/mL in control group， and the difference between the two groups was statistically significant（ Z=-6.387， P＜0.001）. Spearman correlation analysis showed that plasma APN levels in case group did not correlate with the duration of depressive disorder（ P ＞ 0.05） and were negatively correlated with the HAMD-24 score with a statistical difference（ r=-0.266， P＜0.001）. Multifactorial Logistic regression analysis showed that plasma APN was an influencing factor in the occurrence of depressive disorders， and the difference was statistically significant［ OR=3.500， 95%CI（ 1.600，6.300）， P＜0.05］. The area under the ROC curve for plasma APN levels to diagnose depressive disorders was 0.766. Conclusions Plasma APN levels are reduced in patients with depressive disorders and correlated with the severity of depressive disorder. Plasma APN levels are effective in the diagnosis of depressive disorders.