A 42-year-old man was admitted with hematuria after a common cold. No purpura could be observed but there was oozing on the site of the forearm where blood had been taken in a previous hospital. Platelet count was 292 x 10(3)/microliter, examination of coagulation system showed abnormalities; prolonged prothrombin time: PT (99.7 sec) and activated partial thromboplastin time: APTT (more than 200 sec), which suggested deficiency of coagulation factor II (FII), factor V (FV) or factor X (FX). In fact, the FV activity was only 2% of the pooled normal plasma. Mixing test of patient's plasma with normal pooled plasma revealed the existence of an FV inhibitor (FVI), which was IgA with an activity levels of 3 Bethesda unit/ml. Although hematuria stopped soon after beginning treatment with steroids (PSL), the abnormalities in PT and APTT improved very slowly and incompletely. At the time of writing, FVI is still observed ten months after onset. The patient had no underlying disease, and in this case FVI appeared following a common cold. Previous reports have said that FVI can cause mild bleeding, and it disappear in a short time. This case showed the possibility of the hidden presence of FVI in patients with hematuria.