We propose to perform neutron diffraction experiments on single crystals, 3R-AgFeO2 and 2H-AgFeO2 on WISH. Recently, we have studied magnetic orderings and ferroelectricity of the polytypes with powder samples. [N. Terada et. al, PRL 109 097203 (2012), and PRB 91 094434 (2015)] These studies demonstrated that a contribution, p∝Si X Sj, plays important role for understanding appearance of ferroelectric polarization, which is added to conventional inverse Dzyloshinskii-Moriya (DM) term p∝eij X (Si X Sj), in cases of special symmetry conditions. These polytypes give a good opportunity to study the extended inverse-DM effect due to different parent space group (R-3m (3R) and P63/mmc (2H)). In this study, we would like to perform the detail magnetic structural determinations by using 3R and 2H-AgFeO2 single crystals, in order to verify the extended inverse-DM mechanism.