The present article describes the development of a Japanese version of the Early Childhood Behavior Questionnaire (ECBQ). The influence of social desirability on the Japanese ECBQ was investigated using a cross-sectional sample ( N = 318). The effects of gender and developmental changes in temperament were investigated in a longitudinal sample ( N = 191). A three-factor structure was found in the instrument, the three factors being Surgency/Extraversion, Negative Affectivity, and Effortful Control. These factors were the same as those found in the original ECBQ. Social desirability showed less influence on the Japanese ECBQ, indicating the instrument was free from culture-based construct bias. This longitudinal study highlighted that Japanese toddlers have quieter, more withdrawn, and more passive temperaments, a finding that supports that of previous research comparing temperament-scale means between Japanese and U.S. children.