Fibers made of cellulose (CE) and silk fibroin (SF) are wet spun from solutions in N,N-dimethylacetamide containing 7% LiCl (w/w). Different coagulation baths (water and ethanol) and spinning conditions are used. By using water as the coagulant, a partial dissolution of SF occurs and negligible variation of the mechanical properties of the CE-SF fibers with respect to the CE fibers is found. Fibers coagulated in ethanol are dimensionally homogeneous and show better properties. A modulus of about 13 GPa and elongation to break of 16% for the blend containing 30% (w/w) SF are obtained with a 20-mm air gap. The fibers are characterized by FTIR micro-Raman, scanning electron microscopy, and wide- and small-angle X-ray analyses. In particular, the X-ray results show that CE-SF fibers are amorphous with a homogeneous dispersion of small SF domains (1.3 nm) in the CE matrix. These results confirm the good compatibility between the two natural polymers. (c) 2007 Wiley Periodicals, Inc.