A magnetic CdS quantum dot (Fe3O4/polydopamine (PDA)/CdS) was synthesized through a facile and convenient method from inexpensive starting materials. Characterization of the prepared catalyst was performed by means of FTIR spectroscopy, XRD, SEM, TEM, energy‐dispersive X‐ray spectroscopy, and vibrating‐sample magnetometer techniques. Fe3O4/PDA/CdS was found to be a highly active photocatalyst for the amidation of aromatic aldehydes by using air as a clean oxidant under mild conditions. The photocatalyst can be recovered by magnetic separation and successfully reused for five cycles without considerable loss of its catalytic activity. Going greener: Magnetic CdS quantum dots are designed for application as an efficient photocatalyst for the oxidative amidation of aldehydes by using air as the oxidant under mild conditions. The photocatalyst can be recovered by magnetic separation and successfully reused in five cycles without considerable loss of catalytic activity.