Diaphragmatic paralysis is a recognized complication after pediatric cardiac surgery. It is universally acknowledged that direct phrenic nerve injury during surgery is the etiology. However, we experienced two unusual cases of diaphragmatic paralysis following malposition of chest tube placement after pediatric cardiac surgery. The malposition of too deeply placed chest tube with resultant phrenic nerve injury was presumably the underlying cause. One patient underwent successful diaphragmatic plication due to intractable respiratory distress. The other was asymptomatic. Our report highlights the previously unreported complication of chest tube-induced phrenic nerve injury following its malposition after pediatric cardiac surgery. Prompt recognition and correction of tube malposition or selection of a softer chest tube probably can ameliorate the problem.