Background: Activated partial thromboplastin time (aPTT) assays can be affected by plasma antiphospholipid antibodies (aPLs), but the degree of the interference is not easy to predict. This study aimed to investigate the effects on aPTT assay results of different types and combinations of aPLs, including anti-beta(2)-glycoprotein I antibodies, anticardiolipin antibodies and lupus anticoagulant. Materials and Methods: We retrospectively collected clinical information and laboratory tests from aPL-positive patients. The potential influence of aPLs on aPTT assays was assessed. Resuls: The survey included 589 aPL-positive patients. No significant differences existed in basic characteristics such as sex, age, prothrombin time, fibrinogen and alanine aminotransferase among different cases with 1, 2 or 3 types of positiveaPL markers (P > 0.05). In 113 patients with abnormal aPTT values, multivariable linear regression analysis showed a significant correlation between an abnormal degree of aPTT values and dilute Russell viper venom time (dRWT) or silica clotting time (SCT) with a correlation coefficient of 0.437 or 0.497 (P < 0.01), whereas age, anticardiolipin antibodiesimmunoglobulin G, anticardiolipin antibodies-immunoglobulin M and anti-beta(2)-glycoprotein I antibodies were of no significance (P > 0.05). Among blood samples with 3 types of aPLs positivity, the rate of abnormal aPTT detection values was 55.3%, which was significantly higher than that observed in patients with negative, single-positive or double-positive aPL markers (P < 0.05). Patients with a moderate to strong dRWT or SCT had a higher proportion of abnormal aPTT assays than did patients with a low dRWT or SCT (P < 0.05). Conclusions: When abnormal aPTT values are obtained, the influence of aPLs should be considered, especially in the presence of a moderate to strong dRWT or SCT.