Plant growth is greatly affected by low temperature. Cold shock elicits an immediate increase in free Ca²⁺ concentration in plant cells. Here, we focused on the expression of CBF1 under low temperature treatment and the cold-triggered Ca²⁺ responses in CBF1-overexpressing Arabidopsis. CBF1 was induced by low temperature. To address the relation between CBF1 and Ca²⁺, we measured cold-triggered Ca²⁺ responses in CBF1-overexpressing Arabidopsis. CBF1-overexpressing plants exhibited a higher mean peak Ca²⁺ concentration than did wild-type plants, but the Ca²⁺ signature adjacent to the vacuolar membrane increased to similar levels in both plants. In Arabidopsis seedlings pretreated with EGTA or LaCl₃, the cold shock-induced increase of Ca²⁺ concentration was inhibited. The cytoplasmic Ca²⁺ concentration in CBF1-overexpressing and wild-type plants decreased to the same level. Thus, the results suggest that Ca²⁺ is involved in the process of the CBF1 response to low-temperature signal transduction, and the CBF1-overexpress may enhance freezing tolerance of plants by increasing the cytoplasmic free Ca²⁺ concentration.