Purpose: Procalcitonin (PCT), a precursor of calcitonin, has been described as a biomarker of bacterial infection and inflammation. This study was performed to evaluate the clinical usefulness of PCT levels and to reduce the unnecessary usage of antibiotics in children with lower respiratory tract infection (RTI). Methods: Eighty-eight children, with lower RTI, under the age of 5 years, who were admitted to Chungnam National University Hospital, between May 2010 and December 2010, were enrolled. White blood cell counts, erythrocyte sedimentation rate, C-reactive protein, and PCT were measured. Blood and sputum cultures were performed to identify the causative bacteria and reverse transcription-polymerase chain reaction for the viruses. Clinical features were reviewed, retrospectively. Results: The mean participant age was 1.9±1.5 years. The cut-off value for serum PCT levels, which was derived from the receiver-operator characteristic curve, was 0.11·ng/mL. In 29 patients (33.0%) with low PCT levels (<0.11 ng/mL), antibiotic therapy showed no benefit for clinical and laboratory findings. However, in 59 patients (67.1%) with high PCT levels (≥0.11 ng/mL), hospitalization (P=0.005) and fever (P=0.054) exhibited a shorter duration, after antibiotic therapy. Conclusion: A single initial serum PCT levels (≥0.11 ng/mL) may be clinically useful to give a guideline for antibiotic treatment in children with lower respiratory tract infection and to reduce the unnecessary usage of antibiotics.