The hypertensive encephalopathy is one of sudden convulsive cause in patients with acute post-streptococcal glomerulonephritis, but commonly, after the episode we can observe only mild to moderately hypertension in APSGN at ER. So these remains some question of what causes the convulsion in patients with APSGN. In this article, we report 3 cases of convulsion in APSGN with only moderate hypertension, the etiology of which proved to be due to hypertensive encephalopathy by the brain MRI. We believe that the brain MRI is a very useful test to diagnose the etiology of convulsion in APSGN and if brain edema in occipital lobe is detected by brain MRI, the convulsion would be due to hypertensive encephalopathy and the prognosis will be very good.