The (Zr1-x T x )3Al3C5 (T = Hf, Nb, and V) series can be potential candidates to extend the domain of MAX phases. In this work, the structures and properties of (Zr1-x T x )3Al3C5 (T = Hf, Nb, and V) are studied using first-principles calculations. The obtained structural parameters are in good accordance with previously reported data in the literature. Based on the phase stability investigations, the potentially stable layered (Zr1-x T x )3Al3C5 (T = Hf, Nb, and V) solid solutions are proposed, which confirms that Zr3Al3C5 and Hf3Al3C5 can be synthesized. The substitution, especially with group VB transitional metals, endows layered (Zr1-x T x )3Al3C5 series with greatly enhanced mechanical and thermal properties. It is indicated that the bulk modulus B of all the three systems increase with increasing substitution concentration x. A significant increase in the ratio of bulk modulus to shear modulus, B/G, is found with increasing V concentration, which corresponds to the improved ductility. Moreover, solid solutions with V substitution, (Zr1-x V x )3Al3C5, yield a larger effect on thermal conductivity with respect to x, indicating flexible modulation of the thermal conductivity of (Zr1-x V x )3Al3C5 by V substitution can be achieved, which may promote them as promising coating materials. The intrinsic mechanism involved in the enhancements of the mechanical and thermal properties were elucidated through thorough electronic band structure analysis. The difference in the electronic structure and bonding between Zr and T in (Zr1-x T x )3Al3C5 compounds are shown to account for the abnormal variations in their properties.