This　paper　presented　a　design　of　fuzzy　controller　for　a　semi-active　variable　stiffness　control　system.　A　variable　domain　method　was　proposed　for　the　determination　of　system　basic　domain.　Mamdani　methodology　was　used　for　the　fuzzification　of　input　variables.　Three　different　membership　functions,　triangle　membership　function,　Gaussian　membership　function　and　II　shape　membership　function,　were　selected　and　finalized　for　the　study.　A　double-input　and　single-output　control　rule　was　proposed　with　consideration　of　dynamic　characteristic　of　building　structure　and　earthquake　dynamic　characteristic.　Gravity　model　method　was　selected　and　finalized　for　fuzzy　judgment.　©　2011　IEEE.