Objectives <p>Primary spontaneous pneumothorax (PSP) is a condition that primarily affects young patients and has a high recurrence rate. While surgery is the treatment option associated with the lowest recurrence rate for PSP, some patients experience long-term chest drain placement due to prolonged air leak. Our study aimed to elucidate the relationship between coagulation abnormalities and prolonged postoperative air leak in PSP.</p> Methods <p>Patients who underwent surgery for PSP were retrospectively reviewed. Patients were divided into the exploratory and the validation cohorts. From the exploratory cohort, patients with prolonged chest drain placement were identified as the air-leak prolonged (AL-P) group, and the Control group matched at a 1:4 ratio was selected using propensity score matching.</p> Results <p>In the exploratory cohort, 15 patients were assigned to the AL-P group and 60 to the control group. Among the coagulation markers including prothrombin time, activated partial thromboplastin time (APTT) and platelet count, univariate analysis revealed a significantly prolonged APTT in the AL-P group (median 33 vs. 31&#xa0;s, odds ratio 1.26, <i>p</i> = 0.006). Multivariate analysis identified prolonged APTT as an independent risk factor for prolonged chest drain placement. Receiver operating characteristic curve of APTT values for predicting the incidence of prolonged chest drain placement showed a cutoff of 31.5&#xa0;s. In the validation cohort, patients with an APTT ≥ 31.5&#xa0;s showed significantly longer chest drain placement (<i>p</i> = 0.03).</p> Conclusions <p>Our study suggests a potential association between prolonged APTT and prolonged postoperative chest drain placement in patients with PSP.</p>