The effect of substrate strain on the electronic valence band structure of La_0.7Ca_0.3Mn_O3 (LCMO) thin films has been investigated. For this purpose La_0.7Ca_0.3Mn_O3 thin films have been simultaneously grown on SrTiO₃ (STO) and LaAlO₃ (LAO) substrates using pulsed laser deposition technique. The chemical characterization of these samples was carried out by core level x-ray photoelectron spectroscopy, and the structural characterizations by x-ray diffraction. Our experiments confirmed that all these samples have same chemical composition but different strain configuration. The electronic structure of these samples is probed through valence band spectroscopy measurements on Indus-1 synchrotron x-ray source. We observe that strain has large effect on the valence band of La_0.7Ca_0.3Mn_O3. The results are explained on the basis of change in the crystal field splitting due to Mn-O bond length The lattice parameters for powder sample of La_0.7Ca_0.3Mn_O3 (Pbnm space group) are a = 5.451, b = 5.4668 and c = 7.70 Å, where as the lattice parameters of SrTiO3 and LaAlO3 are 3.90 and 3.78 Å respectively. Therefore, it is natural to expect that the c-axis oriented LCMO will grow on the a-b plane along the diagonal of substrate unit cell and will occupy four such unit cells. Thus the film grown on STO and LAO substrates will have in plane expansive strain and compressive strain respectively. In the case of perovskite manganites six oxygen atoms surround the Mn atom in an octahedral cage, thus film on the STO substrate will have longer in plane Mn-O bond length than that of the film on LAO substrate. Thus the potential experienced by Mn ion due to neighboring four in plane oxygen anions will be more in the case of LAO substrate than that of the STO substrate. Therefore, there will be more crystal field splitting of Mn-3d i.e. Δ(t_2g–e_g) in LCMO on LAO substrate than that on the STO substrate. Table 1 summarizes the crystal field parameters obtain from the VBS. It appears that the binding energy associated with e_g (itinerant) electron and the difference Δ(t_2g–e_g) critically depend on the strain condition. The present experimental studies reveal that the strain has large effect on the valence band structure. Therefore, the co-occurrence of different types of strain in a system will lead to the electronic phase separation as suggested by Ahn et al (K. H. Ahn, T. Lookman, and A. R. Bishop J. Appl. Phys. 99, 08A703 (2006).