Convulsion is one of the most common problems in children and hypocalcemia is one the most frequent etiological items in children’s convulsion. Corrected QT (QTc) in EKG is prolonged in hypocalcemia, so it can be a useful tool for evaluation of serum ionized calcium. In three groups (first seizure, multiple seizures, without seizure or control ) every 25 cases, QTc, serum ionized ca, total ca, ABG, and serum albumin level have been checked in the Department of Pediatrics of Imam Khomeini Hospital and outpatient department of Ahari children’s medical center in 2008. Prolonged QTc was observed in 72% of convulsive children (36 cases) but only 19% of non-convulsive children (5 cases) showed this pattern. Ionized calcium was significantly higher in non-convulsive than convulsive groups. There was no correlation between prolonged QTc and total serum calcium; however, this correlation with low ionized calcium was significant. QTc is an easy and rapid method for serum ionized calcium evaluation.