Breast cancer (BC) is one of the leading fatal diseases affecting females worldwide. Despite the presence of tremendous chemotherapeutic agents, the resistance emergence directs the recent research towards synergistic drugs' combination along with encapsulation inside biocompatible smart nanocarriers. Methotrexate (MTX) and 5-fluorouracil (Fu) are effective against BC and have sequential synergistic activity. In this study, a core-shell nanocarrier composed of mesoporous silica nanoparticles (MSN) as the core and zeolitic imidazolate framework-8 nano metal organic frameworks (ZIF-8 NMOF) as the shell was developed and loaded with Fu and MTX, respectively. The developed nanostructure; Fu-MSN@MTX-NMOF was validated by several characterization techniques and conferred high drugs' entrapment efficiency (EE%). In-vitro assessment revealed a pH-responsive drug release pattern in the acidic pH where MTX was released followed by Fu. The cytotoxicity evaluation indicated enhanced anticancer effect of the Fu-MSN@MTX-NMOF relative to the free drugs in addition to time-dependent fortified cytotoxic effect due to the sequential drugs' release. The in-vivo anticancer efficiency was examined using Ehrlich ascites carcinoma (EAC) animal model where the anticancer effect of the developed Fu-MSN@MTX-NMOF was compared to the sequentially administrated free drugs. The results revealed enhanced anti-tumor effect while maintaining the normal functions of the vital organs as the heart, kidney and liver.