The elementary excitations from the conventional magnetic ordered states, such as ferromagnets and antiferromagnets, are magnons carrying spin-1. In a quantum spin liquid, the spin-1 excitations are fractionalized into two deconfined spinons with spin-1/2, which is considered to be a key feature of spin liquids. In this talk, I will present our theoretical investigations on the fractionalized spin excitations in the edge ferromagnetic state of graphene signifying the ferromagnetic Luttinger liquid ground state, the possible emergency of partially deconfined spinons in the square-lattice J1-J2 Heisenberg mode and its evolution with J2, and the coexistence of fractional spin excitations and magnons in the Kitaev-(off-diagonal) model which is suggested to be the minimum spin model for-RuCl3 by us.