It is shown that an etch pit on a crystal may be originated from one of the two causes. The first cause is a microscopic pit or an easily soluble minute portion or inclusion which exists accidentally and locally on the crystal surface, and the other is a dislocation existing in the crystal. In the etch pit originated from the first cause its depth is unchanged but its calibre increases as dissolution or etching proceeds (the temporary or short-time etch pit), while both the depth and calibre of the etch pit originated from the second cause increase in proportion to the etching time (the permanent or dislocation etch pit). A brief consideration is also made of the mulitiplicated etch pit as a variation of the dislocation etch pit. Experimental evidences for the considerations are presented
