Aim: We aimed to investigate whether serum apelin-13 value could be a novel biomarker in the diagnosis of pulmonary thromboembolism (PTE). Material and Method: The study included 142 patients. 82 of which were diagnosed with PTE and 60 were control cases. Serum apelin-13 level was measured using venous blood samples with the ELISA kit. Results: The serum apelin level was 2219.4 +/- 65.2 ng/mL in the PTE group and 1234.7 +/- 35.5 ng/mL in the control group (p<0.05). Serum apelin-13 was 2495.8 +/- 738.0 ng/mL in the DVT (+) group and 2118.0 +/- 496.8 ng/ml. in the DVT (-) group (p=0.009). The best cut-off value for apelin-13 in the control and PTE groups was determined as 1579 ng/mL Sensitivity was 92.7% and specificity was 96.7% (95% confidence interval: 0.939 to 0.995, area under ROC curve: 0.979, p<0.001). Discussion: This study showed that serum apelin-13 value can be used as new diagnostic biomarker in patients with PTE. Apelin-13 value also elevates in patients with DVT (+). These results suggest that apelin-13 value may be used as a novel biomarker in the patients with acute PTE and DVT (+) in future practice.