Three new Gd-III based. coordination polyinets [Gd-2(C2H6SO)(SO4)(3)(H2O)(2)](n) (1), {[Gd-4(Hcoo)(2)(SO4)(5)-(H2O)(6)center dot H2O}(n) (2), and [Gd(HCOO)(SO4)(H2O)] (3) were obtained by modifying gadolinium sulfate. With the gradual increase of the volume ratio of HCOOH and DMSO in-synthesis, the formate anions begin to coordinate with metal centers; this results in the coordination numbers of sulfate anion increasing and the contents of water and DMSO molecules decreasing in target complexes. Accordingly, spin densities both per mass and per volume were enhanced step by step, which are beneficial for the magneto-caloric effect (MCE). Magnetic studies reveal that with the more formate anions present, the larger the negative value of magnetic entropy change (-Delta S-m) is. Complex 3 exhibits the largest -Delta S-m = 49.91 J kg(-1) K-1 (189.51 mJ cm(-3) K-1) for T = 2 K and Delta H = 7 T among three new complexes.