Controlling　the　grain　growth　and　grain　boundary　morphology　is　of　great　importance　in　the　manipulation　of　electrical　properties　of　electro-ceramics.　However,　it　has　been　a　challenge　to　achieve　dense　varistor　ceramics　with　grain　sizes　in　submicrons　and　nanometers　using　conventional　thermal　sintering　at　high　temperatures.　Here　we　present　a　strategy　to　fabricate　dense　ZnO　based　ceramics　with　controlled　grain　growth　and　thin　grain　boundaries　using　cold　sintering　process　(CSP).　With　CSP,　the　sintering　temperature　of　ZnO　based　ceramics　dramatically　drops　from　1100　°C　to　300　°C.　The　Bi2O3,　Mn2O3,　and　CoO　dopants　suppress　the　grain　growth　of　ZnO　under　CSP　conditions,　and　Bi-rich　intergranular　films　(25　nm)　can　be　observed　along　grain　boundaries.　The　cold　sintered　ZnO-Bi2O3-Mn2O3-CoO　ceramic　shows　a　non-linear　coefficient　of　33.5,　and　a　superior　breakdown　electric　field　of　3550　V/mm.　This　work　thus　demonstrates　that　CSP　is　a　promising　technique　for　designing　new　submicron-/nano-ceramics　with　superior　performances.　©　2020　Elsevier　Ltd