This study attempted to identify the effects of age of the first smartphone use and length of the time of first smartphone use on preschoolers behavior problem. To analyze the effect, latent growth model was adapted to KICCE s data (2012∼2014), assessed 432, aged 4, 5, 6 years old. The result showed as below. First the trajectories of behavior problem was identified negatively by the time. It means hat the higher the first behavior problem is, the less rate of slop is. Second, the length of time spending of the first smartphone use influenced intercept and slope of the behavior problem, whereas the age of the first smartphone use only influenced slope. As a result, it is harmful to spend long hours at the first time of using smartphone on slope of the behavior problems. And when the age at first smartphone use was so young, it has negative impact on preschoolers slope of the behavior problems, as time goes by.