The present study was conducted to evaluate in vivo anticancer activity of two novel mononuclear ruthenium(II)compounds, namely Ru(1,10-phenanthroline)2(2-nitro phenyl thiosemicarbazone)Cl2 (Compound R1) andRu (1,10-phenanthroline)2(2-hydroxy phenyl thiosemicarbazone)Cl2 (Compound R2) against Ehrlich ascitescarcinoma (EAC) mice and in vitro cytotoxic activity against IEC-6 (small intestine) cell lines and Artemiasalina nauplii using MTT [(3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide)] and BLT [brineshrimp lethality] assays respectively. The tested ruthenium compounds at the doses 2 and 4 mg/kg body weightshowed promising biological activity especially in decreasing the tumor volume, viable ascites cell counts andbody weights. These compounds prolonged the life span (% ILS), mean survival time (MST) of mice bearing-EAC tumor. The results for in vitro cytotoxicity against IEC-6 cells showed the ruthenium compound R2 to havesignificant cytotoxic activity with a IC50 value of 20.0 μg/mL than R1 (IC50=78.8μg/mL) in the MTT assay and theLC50 values of R1 and R2 compounds were found to be 38.3 and 43.8 μg/mL respectively in the BLT assay. Thebiochemical and histopathological results revealed that there was no significant hepatotoxicity and nephrotoxicityassociated with the ruthenium administration to mice.