ZnO-based　varistors　have　been　widely　applied　in　surge　protection　devices　because　of　their　excellent　nonlinear　current-voltage　(I-V)　characteristic　and　energy　absorption　ability.　Manganese　is　always　added　into　ZnO-based　varistors　in　order　to　enhance　the　nonlinear　characteristic　of　materials.　In　the　present　work,　the　dielectric　properties　of　Mn-doped　ZnO-Bi2O3　varistors　at　extremely　low　temperatures　(20K　similar　to　100K)　were　investigated.　According　to　the　XRD　results,　all　the　samples　exhibit　the　same　overall　phase　structures,　comprising　regularly　ZnO　grain,　Bi-rich　phase.　The　SEM　photos　show　that　the　average　grain　size　of　ZnO　grain　increases　at　first　and　then　decreases.　For　the　dielectric　properties　of　samples　in　the　temperature　range　of　20K-100K,　the　complex　permittivity　show　different　variation　trends　with　the　increase　of　frequency.　The　doping　of　Mn　element　(1　mol%)　will　lead　to　the　appearance　of　relaxation　processes.　Two　relaxation　processes　with　the　activation　energies　of　0.03eV　and　0.007eV　are　observed　in　the　sample.　However,　only　one　relaxation　process　with　the　activation　energy　of　0.03eV　is　detected　from　the　sample　with　1.5　mol%　Mn.　Further　increase　of　Mn　amount　(2　mol%)　can　eliminate　all　the　relaxation　process.　The　results　demonstrate　that　dielectric　spectroscopy　measurement　below　liquid　nitrogen　temperature　can　provide　abundant　information　about　the　shallow　defects　in　ZnO-based　varistors.　At　the　temperature　region　between　20K　and　100K,　new　relaxation　process　can　be　detected　which　offering　new　understanding　to　the　defect　structures　of　materials.　Moreover,　the　doping　amount　of　Mn　element　will　influence　the　dielectric　properties　and　defect　structures　of　ZnO-based　varistors.