This study details the synthesis of high-quality Cd1-x Fe x S nanoparticles using a simple cost-effective chemical technique in the air atmosphere. The structural analysis revealed the presence of a cubic cadmium sulfide (CdS) lattice with a hexagonal iron (II) sulfide (FeS) phase in Cd1-x Fe x S nanoparticles. X-ray diffraction results showed that the iron (III) chloride (FeCl3) dosage had a significant influence on the formation of ternary Cd1-x Fe x S nanoparticles. The morphological analysis indicated that the Cd1-x Fe x S nanoparticles had a spherical shape with a size of approximately 20 nm, while cadmium sulfide nanoparticles had a size of approximately 12 nm. The optical characterization revealed that the band gap of pristine cadmium sulfide and Cd1-x Fe x S nanoparticles decreased with an increase in iron (Fe) content. The band gap of Cd0.8Fe0.2S was slightly higher than that of cadmium sulfide, while the band gaps of Cd0.6Fe0.4S and Cd0.4Fe0.6S nanoparticles were lower than that of cadmium sulfide. The energy band structures of pristine cadmium sulfide and Cd1-x Fe x S nanoparticles were calculated using the density functional theory and were compared with experimental results. In summary, this work presents a detailed investigation of the structural and optical properties of Cd1-x Fe x S nanoparticles synthesized using a cost-effective chemical technique. The results demonstrate the potential application of these nanoparticles in various fields such as optoelectronics, energy harvesting and catalysis.