The　Bi　and　the　Te　nano-powders　are　prepared　by　inert　gas　protected　evaporation-condensation　method;　the　n-type　Bi2Te3　bulk　materials　with　nano-layer　and　twin　crystallite　sub-structures　are　then　synthesized　by　mechanical　alloying　and　spark　plasma　sintering　technique.　The　effects　of　grain　size　and　microstructure　on　thermoelectric　property　are　also　systematically　studied.　The　SEM　and　the　TEM　analyseis　show　that　the　nano-layered　Bi-2　Te-3　bulk　materials　with　twin　crystallite　sub-structures　could　be　fabricated　by　controlling　the　preparing　procedures.　The　thermoelectric　property　result　shows　that　the　thermal　conductivity　is　lowered　compared　with　that　of　bulk　material　of　coarse-grained　starting　powders.　The　thermal　conductivity　decreases　from　1.80　W/mK　to　1.19　W/mK　at　423　K,　the　lattice　thermal　conductivity　decreases　from　1.16　W/mK　to　0.61　W/mK　at　423　K,　indicating　that　the　phonon　scattering　could　be　enhanced　due　to　the　coexistence　of　nano-layer　and　twin　crystallite　sub-structures,　leading　to　reduced　phonon　thermal　conductivity.　The　dimensionless　figure　of　merit　ZT　reaches　0.74　at　423　K　for　bulk　materials　sintered　at　693　K.