Long-time average spectrum (LTAS) was used to analyze the cry utterance of 26 infants under four months old; 16 of them were full-term and the other 10 infants were preterm. The results of first spectral peak (FSP), mean spectral energy (MSE), spectral tilt (ST), high frequency energy (HFE) were used to compare the cry production between term and preterm infants. In addition, cry duration and percent phonation were also compared. According to previous studies, cry production of term and preterm infants show significant differences because immature neurological development of preterm infants. Major findings in this study are: 1) no significant difference in unedited cry duration across groups; 2) no significant difference in percentage of cry utterance across groups; 3) no significant difference in FSP across groups, and higher FSP in term infants; 4) no significant difference in MSE across groups, and a decrease of MSE in both groups over time; 5) no significant difference in ST across groups, and a quicker reduction of energy with larger ST in preterm infants over time; 6) no significant difference in HFE across groups, and a significant decline of HFE over time in both groups. Systematic characterization of infant cry can help to estimate health condition of infants in order to provide appropriate care.