Japanese and Thai preschool children were shown the same visual displays of moving objects and asked to compare the speed of those movers. The results significantly indicate that Thai children show less of a tendency to judge the speed by the temporal precedence, as compared with Japanese children. The present study has also shown that there were more observable tendencies to judge the length of time, or duration by the length of distance in Japanese kindergarten children than in Thai kindergarten children. The above results can be explained well by the effect of their mother language they use; the linguistic differentiation in Thai gave rise to differentiations in Thai preschool children's conception of speed and duration.