Natural rubber (NR), cis-1,4-polyisoprene, has remarkable mechanical properties which are generally explained by strain-induced crystallization (SIC). SIC is commonly investigated by wide-angle X-ray diffraction (WAXD) (see Murakami et al. 2002, Toki et al. 2003, Trabelsi et al. 2003a, among others, for a more complete review of these works, the reader can refer to Huneau 2011). The great majority of the studies on SIC focuses on uniaxial tension; but as engineering applications involve multiaxial loading conditions, mechanical models must take into account the multiaxiality of the material response; for example, it is well-known that the efficiency of a given constitutive equation for rubberlike materials requires shear or biaxial experimental data (Marckmann and Verron 2006). In this way, the present paper is devoted to the experimental study of biaxial strain-induced crystallization of NR by X-ray diffraction using synchrotron radiation. To our knowledge, this is the second study on the influence of biaxiality on strain-induced crystallization of natural rubber: Oono et al. (1973) studied the orientation of crystallites in a stretched thin film of unfilled vulcanized natural rubber at −27◦C.