<p>Altermagnets, a newly recognized magnetic phase, combine the advantages of ferromagnets and antiferromagnets, exhibiting spin-split bands and time-reversal symmetry breaking without net magnetization. In this work, we investigate quantum transport in <i>d-</i>wave altermagnetic nanoribbons with impurities or defects using both analytical transfer matrix methods and numerical simulations via the Kwant package. We reveal that in the 45° orientation relative to the transport axis, the interplay between altermagnetic field and multiple impurities induces a strong spin-dependent interference, leading to a perfect and pure spin current—where the spin-up transmission approaches unity while spin-down transmission vanishes—without relying on spin–orbit coupling or external magnetic fields. This effect is tunable via impurity/defect geometry and nanoribbon width, offering a scalable route for all-electrical spin current generation and spin-logic applications in emerging altermagnetic materials.</p><p> <b>PACS numbers:</b> 75.50.Ee, 72.10.Fk, 72.25.−b</p>