Viscosity η(p0,T)/mPas of 1-butanol and Diesel fuel blends at temperatures T = (273.15 to 468.15) K are reported with an estimated average / = ±0.35 % deviation in dynamic viscosity. Measurements were carried out using the Anton Paar SVM 3000 Stabinger Viscometer and Anton Paar Rheometer MCR 302. The viscosities of 1-butanol were compared with available literature values. The excess viscosity of blends was calculated and obtained negative dependence of them from mole fractions of 1-butanol was discussed.