Although epidural blood patch (EBP) is an effective treatment for postdural puncture headache (PDPH), the adequate blood volume has not been determined. We reported two cases of EBP for PDPH after caesarean section with spinal anesthesia using ultrasound imaging with a 2-5 MHz convex probe. In case 1, the dura mater was expanded and subarachnoid space was compressed by 8 ml of autologous blood with paresthesia at bilateral L5 area during EBP and blood infusion was finished at 10 ml. In case 2, although the area of the epidural space was unchanged by 17 ml of EBP, contrast of the epidural space was altered in as a mosaic pattern. We conclude that ultrasound imaging is useful to confirm the adequate blood infusion during EBP Therefore, there is a possibility of estimating the optimal blood volume by ultrasound imaging.