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The polarized femtosecond spectroscopies obtained from well characterized (100) and (110) YBa 2 Cu 3 O 7-δ thin films are reported. This bulk-sensitive spectroscopy, combining with the well-textured samples, serves as an effective probe to quasiparticle relaxation dynamics in different crystalline orientations. The significant anisotropy in both the magnitude of the photoinduced transient reflectivity change and the characteristic relaxation time indicates that the nature of the relaxation channel is intrinsically different in various axes and planes. By the orientation-dependent analysis, d-wave symmetry of the bulk-superconducting gap in cuprate superconductors emerges naturally. The crucial and yet controversial issues involved in the superconducting gap symmetry of the cuprate superconductors remain unsettled. Numbers of theories and experiments have been proposed and deployed to track down the nature of the order parameter symmetry of the cuprate superconductors. In general, the obtained results can be roughly classified into two sects 1. Majority of experimental results obtained by surface-sensitive experiments 2-6 , all point to the widely-accepted d-wave symmetry scenario. Nonetheless, recently some bulk-sensitive experiments 7-10 , e.g. the investigation of quasiparticle dynamics by the ultrafast time-resolved experiments, have revealed some disputable features of s-wave symmetry or s-d mixed characters. In particular, very recently, Kabanov et al. 7 compared the calculations on the temperature dependence of the photo-induced transmission amplitude below T c and claimed that the results were more consistent with an isotropic gap in YBa 2 Cu 3 O 7-δ (YBCO). This apparently has revived the extensive interest on this matter. The fact that, in addition to its bulk-sensitive characteristic, there exist intimate correlations between the superconducting gap opening and the amplitude as well as relaxation time of the transient reflectivity change (∆R/R) has made the femtosecond pump-probe technique one of the most powerful tools in studying the ultrafast carrier dynamics relevant to high-T c superconductivities 11-19. It is, thus, desirable to reexamine this issue with the improved femtosecond laser and more carefully characterized samples. In this study, based on the general consensus that the amplitude and relaxation time of the transient reflectivity in picosecond scale below T c are directly associated with the opening of the superconducting gap, we have measured the