Silver ferrite AgFeO2 delafossite powders were synthesized by the co-precipitation method with subsequent thermal treatment. The influence of annealing temperature on structural and electro-kinetic properties was intensively investigated. X-ray diffraction, Fourier-transform infrared spectroscopy, and Mössbauer spectroscopy were used as complementary methods for structural investigations. To obtain information about AgFeO2 thermal decomposition temperature thermogravimetric study was conducted. Moreover, the specific surface area and electro-kinetic properties were studied. Investigations revealed that co-precipitated material is a mixture of two polytypes (i.e., rhombohedral 3R and hexagonal 2H) and contains a large amount of residual water. Post-synthesis thermal treatment allowed us to establish that the optimal temperature of annealing is 573 K and the silver ferrite started to decompose at 773 K. Under the applied conditions, AgFeO2 nanoparticles with the relatively high value of the specific surface area – 25 m2/g were obtained. ζ-potential measurements disclosed iso-electric point at pH 8.5 without regard to the temperature of annealing.