Recent works demonstrated that the superconductivity at two-dimensional (2-D) can be achieved in Li-decorated graphene (Nature Phys. 2012, 8, 131 and Proc. Natl. Acad. Sci. 2015, 112, 11795). Inspired by the progress made in graphene, we predict by using the first-principles calculations that Li-incorporated B monolayers (Li-B monolayers) can be alternative 2-D superconductors. First-principles cluster expansion approach was used to evaluate the structural diversity and energetic stability of the 2-D Li-B monolayers by treating them as ternary Lix⬡yB1-x-y pseudoalloys (⬡ refers to B hexagonal hole). After thoroughly exploring the Li-B configuration space, several well-ordered and stable Li-B monolayers were identified. Detailed analyses regarding the electronic structures and lattice dynamics properties of the predicted Li-B monolayers were performed. Compared with the non-superconducting pure B-sheet, some predicted Li-B monolayers can exhibit the phonon-mediated superconducting properties above the liquid helium temperature.