Porous　silica　ceramics　with　low　dielectric　constant　were　prepared　by　sintering　cobalt-doped　MCM-48　(　molar　ratio　of　Co/Si　=　0,　0.01,　0.03,　0.05　and　0.08)　at　1100　degrees　C　for　2　h.　The　influence　of　cobalt　on　microstructure　and　dielectric　properties　of　ceramics　were　examined.　According　to　XRD　pattern,　the　phase　structure　of　the　ceramics　changed　from　amorphous　to　crystalline　with　cobalt　doping.　When　the　Co/Si　ratio　is　greater　than　0.03,　the　porosity　of　ceramics　increased　with　increasing　cobalt　content.　As　a　result,　the　density　and　dielectric　constant　dramatically　decreased.　The　best　results　are　obtained　at　Co/Si　=　0.08:　density　is　1.21　g/cm(3),　dielectric　constant　is　2.59　and　dielectric　loss　tangent　is　6.67　x　10(-2).