Objective: Diagnosing pulmonary diseases with auscultation of breath sounds in children is often difficult because of its high dependence on the clinician’s experience of special circumstances involving children. The purpose of this study was to analyze the spectrograms of normal and adventitious breath sounds to reproducibly find the appropriate character of breath sounds through a mechanical analysis. Method: Breath sounds of 90 children and adolescents aged 0-14 years (median: 4.5 years) were analyzed. They were recorded with an electronic stethoscope (JABES®). Spectrograms of all breath sounds were drawn, and the characteristics of the spectrograms were studied. Result: A total of 173 records of breath sounds of 90 subjects were categorized into normal, wheezing, rhonchi, wheezing combined with rhonchi, crackling, groaning, squawking, and snoring sounds, including 116, 12, 17, 9, 12, 5, 1, and 1 records, respectively. The spectrogram of normal breath sounds showed a diffuse frequency distribution forming a typical dome shape. For wheezing, rhonchi, and their combination, one or more specific descent lines of certain frequencies were observed during expiration. The lines were not horizontal, unlike previously reported. For crackles, the amplitude was high at certain frequencies, forming a scattered distribution of dots. For groaning sound, multiple polymorphic lines with a high amplitude were tangled during expiration. For squawking sound, various forms of multiple lines with different frequencies were seen at the end of inspi ration. For snoring sound, the frequency was widely dispersed with a high amplitude during inspiration and showed multiple descent lines during expiration. Conclusion: Typical characteristics of normal and adventitious breath sounds were determined from the corresponding spectrograms. Spectrography of more samples would improve our understanding of the characteristics of different breath sounds that are not wellknown to date.