A biocidal composition is provided, which comprise a mixture of the biocides Poly-(hexamethylene-guanidium chloride) and N,N-didecyl-N-methyl-poly(oxyethyl) ammonium propionate, which biocides have a synergistic biocidal effect against bacteria and fungi. Specifically, the provided composition can be as disinfectants and general biocidal products; preservatives; pest control; control; preservatives for food or feedstocks; antifouling products; embalming and taxidermist fluids; and control of other vertebrates; vermin control on domestic animals, livestock or pets; alga control; and products for use in spas or swimming pools.