There is provided a safety valve to release excess pressure from a portable gas container for the prevention of an explosion, wherein, when the internal pressure of a portable butane gas container increases over certain level, the safety valve instantaneously operates to release the excess pressure gas from the container at once through an excess pressure gas outlet, thereby sufficiently lowering the pressure inside the container to prevent the container from exploding The safety valve comprises: a safety valve housing with first and second diameter portions integrally formed in a cylindrical shape, the first and second diameter portions being different from each other in diameter; a shaft with a body, a top projection formed on a top of the body, a gas outflow portion and a gasket locking portion formed at a lower part of the body, the shaft positioned inside the safety valve housing; a stopper with a lower part being open, an upper part being closed except for a center where a through-hole is vertically formed, and a side wall vertically formed along the edge of the upper part to provide a space where the gas releases, wherein the stopper is positioned so that the through-hole receives the top projection and the outer circumferential surface of the side wall is secured to the inner circumferential surface of the first diameter portion of the safety valve housing; a spring fitted around the body of the shaft and positioned between the gas outflow portion of the shaft and the stopper; and a first gasket positioned between the first diameter portion of the safety valve housing and an excess pressure gas outlet 13 of the mounting cup; and a second gasket positioned to be received around the gasket locking portion 323 formed at the lower part of the shaft, so that an upper part of the second gasket is secured to a lower part of the gas outflow portion.