A series of new 1-D organic hybrid lanthanoid thioarsenates [Ln(dap)₂]₂(μ–η¹:η¹:η¹:η¹-AsS₄)(μ–η¹:η¹-As^VS₄)]_n {Ln = Ce (Ia), Pr (Ib), Nd (Ic), and Sm (Id); dap = diaminopropane} have been prepared under solvothermal conditions and structurally characterized. Compounds Ia–d contain two [As^VS₄]³⁻ linkage modes, namely μ–η¹:η¹:η¹:η¹-As^VS₄ and μ–η¹:η¹-As^VS₄, which are linked alternately with [Ln(dap)₂]³⁺ groups into 1-D neutral chains [Ln(dap)₂]₂(μ–η¹:η¹:η¹:η¹-As^VS₄)(μ–η¹:η¹-As^VS₄)]_n, which represent the first examples of 1-D organic hybrid lanthanoid thioarsenates based on two [As^VS₄]³⁻ linkage modes. To learn more about the influence of lanthanide contraction on the formation of lanthanoid thioarsenates, five organic hybrid lanthanoid thioarsenates [Ln(dap)₃As^VS₄] [Ln = Tb (IIa), Dy (IIb), Ho (IIIc), and Er (IIId)] and [Er(dien)₂As^VS₄] (III, dien = diethylenetriamine) are also provided. Both II and III contain neutral lanthanide-centred complexes, where the tetrahedral anion [As^VS₄]³⁻ acts as a chelating ligand to the complex [Ln(dap)₃]³⁺/[Er(dien)₂]³⁺ cation. Their optical properties have been characterized by UV-vis spectra, and the density functional theory calculation of Ia has been performed.