In the Ur III economic texts from Drehem, the following two different types of date expression are used: i) u4-X-kam ii) u4-Xba-zal In this paper, I found that these are not used at random, but show chronologically different distribution. The conclusion I reached is as follows: 1) The type of documents is relevant to the choice of date expression, "šu ba-ti" documents take "u4-X-kam" type. "ì-dab5" documents take "u4-X ba-zal" type in Šulgi's reign, but take "u4-X-kam" type in and after Amarsuen's reign. "ba-zi" documents can take both types. 2) "u4-X ba-zal" type is relatively older than "u4-X-kam" type.