Summary: The aim of the present study was to establish a method for preparing an oral liquid dosage form of sildenafil (SIL) citrate from Revatio^® 20 mg tablets (R-tab) that may be administered to patients in neonatal intensive care units (NICU). Croscarmellose sodium (CCS) in R-tab adsorbs SIL in aqueous solution by Langmuir-type adsorption, and the maximum adsorbed amount of the drug per unit weight of CCS and its constant were 1.45 mmol/g and 0.787 L/mmol, respectively. The adsorption of SIL by CCS was inhibited by the addition of sodium chloride and citric acid at concentrations of 0.05% or higher. A suspension with 0.5 mg/mL of SIL was prepared from R-tab, and sodium chloride and citric acid were added to the suspension at concentrations of 0.05 and 0.9%, respectively. Decreases were observed in drug concentrations in the supernatants of suspensions prepared from R-tab with or without sodium chloride. The reason for these reductions was an increase in pH due to the dissolution of calcium monohydrogen phosphate anhydrous. A SIL oral liquid dosage form for use in NICU was prepared from R-tab by the addition of citric acid to prevent adsorption and maintain pH.