Abstract: An inflatable bag includes a gas cylinder filled with a compressed gas and having a bottle mouth for discharging the compressed gas, a hole-piercing device pressable to pierce into the bottle mouth for letting the compressed gas be discharged out of the gas cylinder, an inner bag surrounding the gas cylinder and the hole-piercing device and having air holes for the passing of the discharged gas, and an inflatable outer bag surrounding the inner bag and inflatable by the gas that is discharged out of the gas cylinder and flows through the air holes of the inner bag. By the above configuration, the inflatable bag is placed in a box around the object to be protected and quickly inflated to form a filling buffer without generating heat, ensuring that the protected object is not easily deteriorated and facilitating recycling and cleaning.