The transition energies, probabilities, and oscillator strengths for the electric dipole (E1) transitions between all levels of the ground state and the low-lying excited states of 1s2nl (n=24, l= s, p, d, f) configurations of Li atom and Li-like ions(Be+, C3+, O5+, Ne7+, Ar15+, Fe23 +, Mo39+, W71+, U89+) have been calculated, using the relativistic atomic computational code GRASP2K, which based on the Multi-configuration Dirac-Hartree-Fock (MCDHF) method. The norelativistic results for all of those transitions have been also obtained for comparative purposes by performing the similar calculations in the non-relativistic limit. The effects of relativity on the E1 transition energies and oscillator strengths of Li-like isoelectronic sequence are discussed with a particular emphasis, and some important conclusions are drawn. Comparison of the present results with other available data is also made, good agreement is obtained.