The objective of the present work was the synthesis of N-(2-(4-substituted phenyl)-4-oxo-1,3-thiazolidine-3-yl)-2-(naphthalene-2-yloxy)acetamide and evaluation of in-vitro anticancer activity. Based on this a new series of compound had been planned to synthesize by reacting β-naphthol, ethyl chloroacetate, hydrazinemonohydrate, ethylalcohol and various aromatic aldehydes in presence of anhydrous potassium carbonate The synthesized compounds were characterized by IR, NMR, and Mass spectroscopy. The in-vitro anticancer studies were carried out against Human Acute Monocytic Leukemia - HL- 60 cell line and Human Breast Carcinoma- MCF- 7 cell lines and MTT assay was used to analyze the cell growth inhibition of the both. The results showed that compound A3, A4, A2, A5, A1,and A6 were possessed a very good anticancer activity (at 20 µg/ml) against both Human Acute Monocytic Leukemia - HL- 60 cell line and Human Breast Carcinoma- MCF- 7 cell lines and doxorubicin (at 10µg/ml) was used as a standard drug for both cancer cell lines. The IC50 values for the synthesized compounds were found to be A3 (IC50 of 2.4µg/ml), A4 (IC50 of 2.6µg/ml), A2 (IC50 of 2.9µg/ml), A5 (IC50 of 3.4µg/ml), A1(IC50 of 3.9µg/ml) and A6 (IC50 of 4.5µg/ml) against Human Acute Monocytic Leukemia - HL- 60 and A3 ( IC50 of 2.3µg/ml), A4 (IC50 of 2.6µg/ml), A2 (IC50 of 2.7µg/ml), A5 (IC50 of 3.3µg/ml), A1(IC50 of 3.1µg/ml) and A6 (IC50 of 4.5µg/ml) against Human Breast Carcinoma- MCF- 7.