The relation between pregnancy outcome and single- or double-positivity of anticardiolipin (aCL) and β2 glycoprotein I (aβ2GPI) in antiphospholipid syndrome (APS) has yet to be clearly documented. In this article, a total of 191 lupus anticoagulant-negative pregnant women with primary APS were retrospectively divided into three groups: aCL+/aβ2GPI−; aCL+/aβ2GPI+; aCL−/aβ2GPI+. All women had received medical therapy consisting of prednisone (10–15 mg/day), low-dose aspirin (50 mg/day), and low molecular weight heparin (40 mg/day). The miscarriage rate in the double-positive group was significantly higher than that in the aCL+/aβ2GPI− group (46.2% vs. 22.1%, p < 0.05); the miscarriage rate in the aCL−/aβ2GPI+ group (36.4%) was not significantly different from the rates of the other two groups (p > 0.05). Thus, double-positivity may be a risk factor for pregnancy loss and aβ2GPI antibody may be a better prognostic marker than aCL antibody for pregnancy outcome.