X-ray diffraction analysis shows that it is difficult to discriminate various kinds of A Fe₃(SO₄)₂(OH)₆(A=K⁺, H₃O⁺) jarosites because their XRD data are very similar to each other. However, a series of jarosites could be discriminated by XRD and EDS method. The XRD result shows that 003 and 107 lattice spacing (d) of the jarosite increases with K⁺ ion content, whereas 033 and 220 lattice spacing (d) decreases with increasing K⁺ ion content. Their relationship is described by the regression equation. The explanation of this result from the crystal structure theory is that K⁺ and H₃O⁺ ions are located in the larger space and distributed along Z axis. Obvious change of jarosite crystal structure in the Z axis occurs with the mutual substitution between K⁺ and H₃O⁺ ions.