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Background: An infant is an individual who possesses his/her own innate personality. Crying is a form of communication, an expression of emotions and temperament. Our study aims to predict an infant’s temperament in the early stage by analyzing the crying sound after painful stimulation of vaccination. Methods: We analyze three types of information: (i) the crying sounds caused by the pain stimuli from being injected with a Hepatitis B vaccine, (ii) the answers provided by the parents in a temperament assessment scale (TAS) questionnaire, and (iii) backend analyses of the audio signals of the crying sounds. These data are subjected to correlation analyses, T-tests, and normal distribution for deriving the relationship between crying and temperament. Results: The results show that the manifestations of an infant’s temperament may be affected by the living environment and feeding habits. A tendency exists for a group of infants with similar and focused crying sounds to have higher average scores for three of nine temperament traits: approach or withdrawal, intensity of reaction, and quality of mood. Conclusions: An infant’s crying sounds in response to a pain stimulus can be used to predict his/her temperament in terms of the three aforementioned traits.