<p>We systematically studied the role of A-site ionic radius and cationic disorder on the structural, magnetic, and magnetocaloric properties of Nd_0.6Sr_{0.4–<i>x</i>}M_<i>x</i>MnO₃ (M=Ca, Ba). The lattice parameters and average A-site ionic radius increase monotonically from Ca to Ba. The Ca/Ba substitution mainly modifies the local A-site chemical environment and disorder degree. All compounds reveal a clear paramagnetic-ferromagnetic transition with the highest Curie temperature <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(T_{C}=263\,\text {K}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>T</mi> <mi>C</mi> </msub> <mo>=</mo> <mn>263</mn> <mspace width="0.166667em" /> <mtext>K</mtext> </mrow> </math></EquationSource> </InlineEquation> for Nd_0.6Sr_0.4MnO₃ and reduced to 197/198&#xa0;K when Sr²⁺ is partially replaced by Ca²⁺ or Ba²⁺. Analysis of their critical exponents shows that Ca- and Ba-substituted samples exhibit short-range ferromagnetic correlations and stronger deviations from mean-field behavior, consistent with enhanced bandwidth narrowing and A-site disorder-induced magnetic inhomogeneity. Magnetocaloric measurements demonstrate that under <InlineEquation ID="IEq20"> <EquationSource Format="TEX">\(\Delta H~ = ~1.0T\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Δ</mi> <mi>H</mi> <mspace width="3.33333pt" /> <mo>=</mo> <mspace width="3.33333pt" /> <mn>1.0</mn> <mi>T</mi> </mrow> </math></EquationSource> </InlineEquation>, the maximum magnetic entropy changes are about 2.545, 4.911, and 3.064&#xa0;J&#xa0;kg^–1&#xa0;K^–1 for Sr, Sr/Ca, and Sr/Ba, respectively, indicating that A-site substitution significantly enhances the magnetocaloric response. These results demonstrate that tuning A-site ionic radius and cationic disorder provides an effective route to control the balance between long-range ferromagnetic order and short-range ferromagnetic/cluster states in Nd-based perovskite manganites.</p>