Nanosized manganese ferrite (MnFe 2 O 4 ) particles were prepared by sol–gel method using natural polymers like wheat flour (WF) and potato flour (PF) as surfactants and its structural, morphological, optical and magnetic characteristics were studied by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), photoluminescence spectroscopy (PL) and vibration sample magnetometer (VSM). Brunauer–Emmett–Teller (BET) surface area test also performed and the results obtained were discussed. The average crystallite size was found to be 23 and 16 nm for WF/MnFe 2 O 4 and PF/MnFe 2 O 4 samples, respectively. Magnetic hysteresis loops confirmed the super-paramagnetic behavior for both the samples. For oxidation of benzyl alcohol to benzaldehyde, the catalytic activity of MnFe 2 O 4 nanoparticles (NPs) was carried out. Antimicrobial and antifungal activity of WF/MnFe 2 O 4 and PF/MnFe 2 O 4 samples were investigated against two Gram-positive bacteria ( Staphylococcus aureus , Streptococcus pneumoniae ), two Gram-negative bacteria ( Pseudomonas aeruginosa , Salmonella paratyphi ) and fungus ( Candida albicans ) using inhibition zone method. Minimum Inhibitory Concentration (MIC) values also calculated to determine susceptibilities of bacteria to drugs and also to evaluate the activity of new antimicrobial agents. The in vitro cytotoxicity of newly synthesized samples were analyzed by MTT assay against MCF-7, A549 and HaCaT cell lines in a dose-dependent fashion. Among these two samples, sample B (using potato flour) shows better response than sample A (using wheat flour) and both the samples were non-toxic to normal cell line. The concentration required to kill 50% of the cell (IC 50 ) was also calculated. Graphical Abstract MnFe 2 O 4 nanoparticles were synthesized by sol–gel method using natural polymers, wheat flour and potato flour, as surfactant. The as-prepared MnFe 2 O 4 was characterized by XRD, FT-IR, SEM, EDX, PL and VSM analysis. The average crystallite size was found to be 23 and 16 nm for WF/MnFe 2 O 4 and PF/MnFe 2 O 4 samples, respectively. Magnetic hysteresis loops confirmed the super-paramagnetic behavior for both the samples. The catalytic activity of MnFe 2 O 4 nanoparticles (NPs) were carried out for oxidation of benzyl alcohol to benzaldehyde. Biological activities like antimicrobial, antifungal and anticancer activities of the samples were investigated. Among these two samples, PF/MnFe 2 O 4 shows better response than WF/MnFe 2 O 4 and both the samples were non-toxic to normal cell line. IC 50  values of WF/MnFe 2 O 4 ( a ) and PF/MnFe 2 O 4 ( b ) against A549 and MCF-7 cell lines