The current study aimed to test the cytotoxic efficacy of silver nanoparticles (Ag-NPs) synthesized using polysaccharide from marine algae Chnoospora minima against Human Breast Cancer (MCF-7) Cells in vitro. The extracted polysaccharide and the synthesized Ag-NPs were analyzed by Fourier-transform infrared spectroscopy (FTIR). Biosynthesized silver nanoparticles (Ag-NPs) were characterized using UV-spectrophotometry, dynamic light scattering (DLS), Zeta Potential, Scanning electron microscopy (SEM), and Energy Dispersive X-ray (EDX). Cytotoxicity was assessed using the Sulforhodamine B assay (SRB assay). A dose-dependent cytotoxic effect with an IC₅₀ value of 3.921 µgmL^-1 was observed for biosynthesized Ag-NPs against MCF-7 compared to the control (IC₅₀:>200 µgmL^-1 ). An absorption peak at 420 nm in UV–vis spectrum proven the formation of Ag-NPs; DSL analysis confirmed the formed particles are within the nanoscale with a Z-Average of 84 d.nm and Zeta potential was -18.5 mV. The SEM imaging showed biosynthesized Ag-NPs have a spherical shape with low aggregation. The EDX spectrometers confirmed the presence of an elemental silver signal of the biosynthesized Ag-NPs. SRB assay demonstrated that the green synthesized Ag-NPs inhibit the proliferation of MCF-7 cells. The present study's innovation is that the green synthesis of NPs, which is cost-effective and straightforward, providing stable nano-materials, an alternate for the large-scale synthesis of silver nanoparticles.