Objective To investigate the perihematomal changes of hyperacute parenchymal hematomas and the clinical value by MRI. Methods Multi-sequence MRI was performed on 4 hematomas in vitro and on 15 pigs with lobar intracerebral hemorrhage (ICH) for about 30～60 min and 3 h respectively. The integrity of blood-brain barrier (BBB) in ICH pigs was assessed by electron microscopy and Evan's blue dye technique. MR scanning was performed on 2 ICH patients proved by CT for 4 and 9 h after onsets. Results FLAIR and T 2-weighted images showed hyperintensity signal around the hematomas in vitro and in pigs with ICH within 1 h, and more obviously at 3 h. When the gelose cavity was cut, plasma was seen around the clot. The perihematomal ADC values of the pigs increased both within 1 and at 3 h after ICH. However, the BBB was intact at 3 h, which was proved by electron microscopy and Evan's blue dye technique. Water-like intensity signal was observed around the hematomas in two patients with acute ICH. Conclusion The perihematomal changes of hyperacute ICH observed on MRI are resulted from the blood clot contraction and the serum formation and extravasation, but not real cerebral edema.