Fetomaternal hemorrhage (FMH), which can occur throughout pregnancy, is still a poorly understood clinical condition. It is very difficult to be timely diagnosed and often results in poor pregnancy outcomes. Here the authors reported two rare cases of silent massive FMH of unknown cause in the third trimester of pregnancy, which presented with non-reactive fetal heart rhythm or decreased fetal movement at the very beginning, and resulted in severe fetal anemia and neonatal deaths. A pregnant woman at late pregnancy with a complain of unspecific signs such as decreased fetal movement should arouse a high index of clinical suspicion of idiopathic FMH, and an urgent ultrasound or lab tests detecting FMH could be suggested. Considering emergent delivery versus expectantly management will depend upon acute or chronic FMH, gestational age, results of fetal testing, availability of experienced personnel, and procedural difficulty.