A tool box includes a first casing, a second casing, at least one fastening member, and at least one first elastic member. The first casing has at least one first receiving slot which has two first restriction portions. The second casing has at least one second receiving slot, a second restriction portion, and a first locking portion. The at least one fastening member has a third restriction portion, a second locking portion, and two fourth restriction portions. The at least one first elastic member is biased between the at least one fastening member and the at least one first receiving slot, and the at least one fastening member is pushed by the at least one first elastic member, such that second locking portion is locked onto the first locking portion to interlock the first casing and the second casing.