Prior research has indicated that spontaneous trait inferences (STIs) occur more easily among fifth graders than among adults, although STIs generally develop only among Westerners. However, no prior studies on STI include Asian children. This study explored the development of STIs among Japanese fifth graders, seventh graders, and undergraduates. Experiments 1 and 2 used a relearning paradigm, and participants' recollections of photo-trait pairs after being presented with congruent behaviours were compared with those after being presented with incongruent behaviours. If participants showed better recollection after being presented with congruent behaviour descriptions (saving effects), this indicated that they had made STIs from the behaviour. The results showed that STIs occur among Japanese children and adults, although their occurrence was associated with a trait valence factor. STIs occurred to a small extent from positive-trait-implying descriptions only among fifth and seventh graders, not undergraduates. In contrast, STIs occurred clearly from negative-trait-implying descriptions in all age groups. The results of Experiment 3, which used a trait-rating task that required less storage capacity of long-term memory, confirmed that fifth and seventh graders, as well as adults, made spontaneous inferences of specific traits implied from behavioural descriptions and not a wide positivenegative framework. The developmental model of STIs depending on trait valence and culture is discussed.