Effects of dimethipin on ${alpha}$-amylase activity of barley seeds were investigated. In the treatments of $1{mu}M;and;10{mu}M$ dimethipin, the indexes of germination were reduced to 17% and 24 % respectively. After seed germination, dimethipin was added to germinated seedlings and then the seedlings were kept to measure seedling length under illumination for 7 days. In control, the length of seedling was 5.7 cm, but in the treatments of $1{mu}M$ dimethipin and $10{mu}M$ dimethipin, seedling lengths were 5.5 cm and 1.2 cm respectively. In the relationship between dimethipin concentrations and ${alpha}$-amylase activities, there was a linear curve. The more dimethipin was added to the seeds, the more ${alpha}$-amylase activities were inhibited. In the treatments of $1{mu}M$ dimethipin and $10{mu}M$ dimethipin, ${alpha}$-amylase activities were reduced to 33% and 71% respectively. Dimethipin also inhibited ${alpha}$-amylase activities increased by gibberellin and the content of soluble protein. Therefore, it could be suggested that dimethipin might inhibit directly the activities of hydrolysis enzymes including ${alpha}$-amylase or the expression of ${alpha}$-amylase genes as germination and seedling growth were severely disturbed.