We study the dependence of the structural properties of uranium monochalcogenides, UX where X = S, Se, and Te, as well as their electronic ones on the exchange-correlation energy functionals within the spin density functional theory, carrying out all electron calculations by the fully relativistic full-potential linear-combination-of-atomic-orbitals method. We employ two functionals of the local spin density approximation (LSDA) and two functionals of the generalized gradient approximations (GGA); the former two are the Perdew-Zunger and Perdew-Wang functionals and the latter two are the Perdew-Burke-Ernzerhof (PBE) and PBEsol functionals. We also examine the effects of the relativistic correction to the LSDA exchange part of each functional. We find that, for lattice constants, bulk moduli, and cohesive energies, the results of the calculations using the PBE functional are in the best agreement with the experimental results. On the contrary, we find that calculated total magnetic moments and one-electron energies are almost the same for all the LSDA and GGA functionals employed in this work, failing to improve the agreement between the calculated and experimental results even if the gradient and relativistic corrections are included. We also find that the relativistic correction plays minor roles in both the structural and electronic properties.