This study aimed to synthesize and characterize nickel magnetic nanoparticles (MNPs), and evaluate their anticancer effects on the DLD1 colon cancer cell line and L929 mouse fibroblast cell line. The characterization of the MNPs which were synthesized by selective leaching was performed with a Zetasizer via dynamic light scattering (DLS) method, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The zeta potential of Ni MNPs was determined to be -24.7(7.83) mV. The size of Ni MNPs was 764 nm with 0.486 PDI value. The cytotoxicity test was performed for L929 Fibroblast cell line and DLD1 colon cancer cell line. Cytotoxicity analyses were performed with the MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The cell viability was observed to be 94.89% for L929 fibroblast cells. Then, anticancer effects on the DLD1 colon cancer cell line were evaluated. The use of Ni MNPs can be effective in reducing the effects of cancer since it decreases the cell viability overall, and it seems even more effective in the cancerous cell lines. We determined the cell viability of the DLD1 colon cancer cell line with the use of 0.001 grams of Ni MNP as 78.2%.