Abstract: Preliminary investigations of Ramalina farinaceae (RF) plant extract sourced from Southeast, Nigeria for later possible antiviral usage lead to the identification of anti-proliferative activities against some mammalian cell lines and mouse splenocytes. The extract/cell systems were incubated for 1-2 days followed by analysis of cell viability status using an MTT-based assay. Measurement of released interferon gamma cytokine was undertaken as a proliferative activation marker for immune cells derived from mouse spleen. The preliminary data showed anti-proliferative cytotoxic activities with TC50 = 103.1, 61.57 and 65.24 μg mL–1 for vero, Tsa201 and A293 cells, respectively, when tested in a concentration-dependent manner. Extract-stimulated mouse splenocytes showed no proliferative activation status contrary to INF-g release recorded for lipopolysaccharide (LPS) stimulated mouse splenocytes. Ramalina farinaceae extract in the present study appear to down-regulate cell proliferation indicating possible utility in counteracting cell hyperplasia. It could however, equally still be utilized in other cellular systems when adequately tailored at lower concentrations in specific given settings to meet the contingent need.