Spaghetti samples were prepared by replacing wheat flour with defatted soy flour (DSF) at 0, 10, and 20% levels (w/w). Each sample had 4% gluten. In addition, xanthan gum was added at three levels (0.0, 0.2, and 0.4%) to spaghetti dough containing 20% soy flour as a modifying agent. Samples were extruded at 35 or 50oC and dried at, respectively, 52oC for 21h or 72oC for 6 hours. The color, protein content, cooking loss, cooked weight, and firmness of all spaghetti samples were measured. A trained sensory group evaluated chewiness, firmness, stickiness, color, and flavor. The overall results showed that increasing protein level in spaghetti caused an increase in the firmness and cooking loss with a decrease in cooked weight and consumer acceptance. However, when xanthan gum was added to spaghetti dough containing 20% DSF, the positive properties of spaghetti, including cooked weight and consumer acceptances, were improved significantly and its negative aspects, including firmness and cooking loss, were reduced noticeably. When xanthan gum and DSF levels reached, respectively, 0.4 and 20%, and the spaghetti dough was extruded at 50oC followed by drying at average temperature of 72oC, the best spaghetti in terms of physico-chemical and organoleptic properties was obtained.