Penggunaan antibiotika yang tepat ialah penggunaan antibiotika yang efektif dengan peningkatan efek terapeutik, sehingga meminimalkan terjadinya resistensi dan meminimalkan biaya obat. Penggunaan antibiotika yang rasional harus memenuhi beberapa kriteria yaitu, tepat pasien, tepat indikasi, tepat obat, tepat dosis, dan tepat lama pemberian. Penelitian ini bertujuan untuk mengevaluasi kerasionalan penggunaan antibiotika pada pengobatan pneumonia anak di Instalasi Rawat Inap RSUD Prof. Dr. W.Z. Johannes, Kupang, periode Januari–Juni 2015. Penelitian ini berupa penelitian deskriptif dengan pengumpulan data secara retrospektif yang didasarkan pada catatan medis. Penelitian dilakukan terhadap 41 catatan medis penderita pneumonia anak yang memenuhi kriteria inklusi. Hasil penelitian menunjukkan jenis antibiotika yang paling banyak digunakan pada pneumonia anak ialah kombinasi antibiotika ampisilin-gentamisin sebesar 46,34% dan ampisilin-kloramfenikol sebesar 14,63%. Evaluasi penggunaan antibiotika berdasarkan kriteria tepat pasien (100%), tepat indikasi (100%), tepat obat (21,95%), tepat dosis (51,22%), dan tepat lama pemberian (53,66%). Terdapat hubungan yang signifikan (p=0,021) antara berat badan dengan kerasionalan penggunaan antibiotika. Appropriate use of the antibiotic is effective use to increase therapeutic clinical effect, minimized the occurrence of resistance, and effective terms of cost. Rational use of antibiotics have to comply with several criteria like the appropriate patient, appropriate indication, appropriate drug, appropriate dose, and appropriate duration. This study was aimed to evaluate the rational utilizing of antibiotics in the treatment of pediatric pneumonia in Hospitalized Installation of RSUD Prof. Dr. W.Z. Johannes Kupang in period January–June 2015. This research is a descriptive study with retrospective data aggregation based on medical records. Research conducted on 41 pediatric patiens medical record with pneumonia who fulfill the inclusion criteria. The result showed that antibiotics are the most used antibiotics combination is ampicillin-gentamicin were 46,34% and ampicillin-chloramphenicol were 14.63%. Evaluation of rational use of antibiotics to the appropriate patient (100%), appropriate indication (100%), appropriate drug (21.95%), appropriate dose (51.22%) and appropriate duration (53.66%). There is a significant (p=0.021) relationship which between weight rasionality use with antibiotics.