Two novel tetra- and deca-nuclear dysprosium compounds, namely, [Dy₄(μ₃-OH)₂(L)₁₀(bipy)₂(H₂O)₂]_n (1) and {[Dy₁₀(μ₃-OH)₈(L)₂₂(bipy)₂(H₂O)₂]·5H₂O}_n (2) (L = 3-fluoro-4-(trifluoromethyl)benzoic acid; bipy = 2,2′-bipyridine), have been successfully obtained by hydrothermal reaction at different pH values. The solid state structures of 1 and 2 were established by the single crystal X-ray diffraction technique, and both of them exhibit complicated 1D chains with [Dy₄] (1) and [Dy₁₀] (2) cluster units, respectively. Adjacent [Dy₄] in 1 and [Dy₁₀] in 2 are connected by two bridging carboxylate groups in the η¹:η¹:μ₂ mode. Magnetic studies reveal that they exhibit different magnetic relaxation behaviors with the energy barrier of 23.6 K for 1 and 3.2 K for 2. Interestingly, the large divergence in both the structures and magnetic properties for 1 and 2 only originated from the different pH values in preparing them.