Infants with cystic fibrosis can develop episodes of hyponatremic, hypochloremic dehydration with metabolic alkalosis, and management is difficult. In this paper, we present a nine-month-old case with cystic fibrosis with pseudo-Bartter syndrome, who was rehydrated with two types of modified oral rehydration solution. Intravenous rehydration was impossible due to inaccessibility of route. With this oral rehydration treatment, her purging rate decreased, and serum sodium levels improved and remained stable. In cases with impossible intravenous route, one of these modified rehydration solutions could be given.