A key mechanism. A base plate includes at least one first guiding base, at least one second guiding base, at least one first barricade, and at least one second barricade. The first guiding base opposes the second guiding base. The first barricade opposes the second barricade. A scissors linking assembly is connected to the base plate and includes a first linking member and a second linking member. The first linking member pivots to the second linking member and includes a first guiding pillar. The second linking member includes a second guiding pillar. The first guiding pillar is disposed in the first guiding base through the first barricade and is abutted therebetween. The second guiding pillar is disposed in the second guiding base through the second barricade and is abutted therebetween. A keycap is connected to the scissors linking assembly.