The mechanical behavior of films cast from sugar beet cellulose microfibrils was investigated through tensile tests. The obtaining of these microfibrils by chemical and mechanical treatments from the raw beet pulp is described. Depending on their purification level, individualization state, and moisture content, differences in tensile modulus are observed. It is found that pectins act as a binder between the cellulose microfibrils, which tends to increase the Young’s modulus in dry atmosphere and to decrease it in moist conditions. The extraction of the cellulose microfibrils from the sugar beet cell wall and the obtainment of microfibril suspensions with partial individualization of the microfibrils by a mechanical treatment lead to the formation of a network of cellulose microfibrils within the film, which in turn increases the tensile modulus. Furthermore, the effect of the remaining pectins is compared with the effect of pectins previously removed and added to completely puri fred cellulosic microfibrils. As expected, once removed and so partly degraded, those pectins have nearly no influence on the mechanical properties.