Biogenic synthesis of iron nanoparticles has been reported in many studies. However, there is no such study that combines antioxidant, antimicrobial, anticancer and dye removal activities of the synthesized iron nanoparticles. The present study focused on the green synthesis and Congo Red (CR) dye removal, cytotoxic, antioxidant and antimicrobial activities of supermagnetic Fe3O4 nanoparticles using Plantago lanceolata L. extracts (PLE@FeNPs). The morphology and physical properties of PLE@FeNPs were characterized by FTIR, XRD, SEM, EDX, TEM and DLS analysis. XRD and zeta potential analysis revealed a potential of-12.2 mV and formation of cubic crystals, with an average dimension of 7 nm, and a wide band at 352 nm was detected in UV-vis spectroscopy. The optimum adsorption conditions of pH, temperature and adsorbent amount for CR removal were found as pH 4, 25 ℃ and 15 mg respectively with a high removal efficiency of 99 %. To evaluate dye adsorption behaviors of the PLE@FeNPs, adsorption isotherm models -Langmuir, Freundlich and Temkin- were applied to the present data. Langmuir Isotherm model (R2 = 0.96, 25 °C) were best fitted to our data. Thermodynamic evaluation of the results showed that the reaction was spontaneous (∆G = -26.6 kJ mol-1) and exothermic (∆H -35, 3 kJ mol-1). PLE@FeNPs showed highest antimicrobial activity on Staphylococcus aureus. Antioxidant activities of PLE@FeNP was examined by DPPH removal (89.79%) and metal-chelating activity (74%). The in vitro cytotoxicity experiments showed that PLE@FeNPs possessed significant cytotoxic effects in human lung cancer (A549) cell line while no such effects were observed on human neuroblastoma (SH-SY5Y) cell line. PLE@FeNPs also caused DNA fragmentation on A549 cells. Overall these results pave the way for further applications in dye removal and biological applications of environmentally friendly PLE@FeNPs.