To provide a disposable diaper for a low body weight infant which allows a low body weight infant to easily move his/her legs, and which has improved fitting of an absorbent core to the low body weight infant.SOLUTION: A disposable diaper 1 for a low body weight infant comprises: an absorbent core 2 with a narrow width part in a center portion of a longitudinal direction, a central width of the absorbent core 2 in the longitudinal direction being 15 mm or greater and 45 mm or smaller. When a length of the diaper 1 in the longitudinal direction in a state of being developed and extended in the longitudinal direction is a product length, and a length in the longitudinal direction of the diaper 1 in a natural state in which the diaper 1 is developed and extended in the longitudinal direction and then placed on a top surface of a stand with its skin-side surface facing downward is an apparent product length, the apparent product length divided by the product length is 0.7 or greater and 1 or smaller.SELECTED DRAWING: Figure 1【課題】低体重児が脚を動かしやすく、かつ、低体重児への吸収性コアのフィット性を向上させた低体重児用の使い捨ておむつを提供する。【解決手段】長手方向の中央部に幅狭部を有する吸収性コア２を備え、長手方向における吸収性コア２の中央の幅は１５ｍｍ以上４５ｍｍ以下である低体重児用の使い捨ておむつ１であり、長手方向に展開かつ伸長した状態のおむつ１の長手方向の長さを製品長とし、おむつ１を長手方向に展開かつ伸長した後に肌側面を下にして台の上面に載せた自然状態のおむつ１の長手方向の長さを見かけ製品長とした場合、見かけ製品長を製品長で除した値は０．７以上１以下である。【選択図】図１
