Deoxyribonuclease I (DNase I) is one of the main nucleases involved in deoxyribonucleic acid (DNA) degradation during apoptosis. It catalyzes the hydrolytic cleavage of DNA, producing 5'-oligonucleotides. The inhibition of DNase I may serve as an important mechanism for protecting DNA against premature degradation during cell damage. Fourteen hydantoin-containing compounds, including two newly synthesized and seven previously synthesized metal complexes, along with five previously synthesized hydantoin ligands, were evaluated in vitro for their inhibitory properties against bovine pancreatic DNase I. As a result, the 3'-methyl-4-thio-1H-tetrahydropyranspiro-5'-hydantoin platinum complex (8) inhibited the enzyme with an ICsub.50 value of 110.20 ± 24.20 µM, a potency 3-fold greater than that of the reference crystal violet (ICsub.50 = 378.27 ± 47.75 µM). To understand the binding mode and mechanism of inhibition of compound 8 with DNase I, molecular docking calculations were performed. The analysis revealed that compound 8 interacts with the most important catalytic residues of DNase I. To the best of our knowledge, this is the first report of a platinum complex inhibiting DNase I.