A protective casing is adapted for a first electronic device with a first button and a second electronic device with a second button. The protective casing includes a lower casing and an upper casing. The lower casing includes a partition member disposed therein. The partition member has a first resilient arm extended from a periphery of the partition member. The upper casing cooperates with the lower casing to form a first accommodating space, wherein the first accommodating space is above the partition member. When the first electronic device is accommodated in the first accommodating space, the first button is at a first distance from a bottom of the partition member. When the second electronic device is accommodated in the first accommodating space, the second button is at a second distance from the bottom of the partition member. A length of the first resilient arm covers the first and second distances.