In　this　work,　we　have　carefully　examined　the　morphology　of　semiconducting　polymer:insulating　polymer　blends,　which　were　deposited　from　inkjet　printing.　We　attempted　to　study　the　impact　of　molecular　weight　(MW)　of　insulating　polymer　on　the　nanoscale　morphology　and　function　of　the　blends.　The　morphology　of　all　of　the　inkjet-printed　samples　was　characterized　by　small-angle　neutron　scattering　(SANS),　grazing　incidence　X-ray　diffraction　(GIXD),　and　atomic　force　microscopy　(AFM).　The　SANS　results　show　that　the　domain　size　of　the　blends　increases　by　increasing　the　MW　of　insulating　polymer,　while　the　domain　purity　reaches　the　maximum　with　proper　molecular　weight　of　insulating　polymer.　AFM　images　show　that　the　connectivity　of　semiconducting　polymer　domains　is　disrupted　with　addition　of　polystyrene　(PS)　with　low　molecular　weight　(Mw　=　2.5K　and　20K),　while　well-interconnected　domains　are　observed　with　addition　of　PS　with　high　molecular　weight　(Mw　=　182K　and　2000K).　GIXD　results　indicate　that　the　π-π　stacking　distance　of　semiconducting　polymer　can　be　shortened　with　addition　of　PS　and　decreases　with　an　increase　of　PS　molecular　weight　from　2.5K　to　182K.　Further　increasing　molecular　weight　of　PS　to　2000K　results　in　very　weak　π-π　stacking　ordering.　This　work　demonstrates　that　the　domain　purity,　connectivity　of　semiconducting　polymer　domains,　and　molecular　packing　are　crucial　for　the　charge　transport.　The　judicious　choice　of　the　MW　of　insulating　polymer　could　carefully　control　the　nanoscale　morphology　of　semiconducting　polymer:insulating　polymer　blends,　which　could　provide　blend　morphology　with　high　domain　purity,　well-connected　domains,　along　with　reduced　π-π　stacking　distance,　all　of　which　facilitate　charge　transport,　resulting　in　a　significant　improvement　of　charge　mobility.　©　2016　American　Chemical　Society.