The upper critical field Hc(2) in superconductivity was investigated for CePt3Si and CeIrSi3 without inversion symmetry in the tetragonal structure. A significant anisotropy of Hc(2) between H vertical bar vertical bar [0 0 1] and H vertical bar vertical bar [1 0 0] was not observed in CePt3Si even at 0.6 GPa as well as ambient pressure, where the Neel temperature with T-N = 2.3 K at ambient pressure becomes zero at 0.6 GPa. The similar result was observed at 1.95 GPa in CeIrSi3, where antiferromagnetism and superconductivity coexist, while a large anisotropy of Hc(2) in CeIrSi3 was observed with increasing pressure: Hc(2)(0) = 300-400 kOe for H vertical bar vertical bar [0 0 1] and Hc(2)(0) = 95 kOe for H vertical bar vertical bar [1 1 0] at 2.65 GPa, which is higher than the critical pressure P-c = 2.25 GPa. A large value of Hc(2) for H vertical bar vertical bar [0 0 1] in CeIrSi3 might become an experimental evidence of the spin-triplet superconductivity in the non-centrosymmetric structure. It is also remarkable that CeIrSi3 is a strong coupling superconductor and the electronic specific heat coefficient is approximately unchanged as a function of pressure even at P-c, which is highly different from the divergent mass enhancement at Pc in a pressure-induced heavy fermion superconductor CeRhIn5.