The revision of regulations for apartment unit design, which are concerning the area calculating criteria (revised in 1998) and use of balcony (revised in 2005), considerably have increased livable space of apartment unit. This paper aims to verify its effect to apartment unit plan in the aspect of number of rooms and size of each room. For this purpose, 60 and 85 $m^2$ sized apartment unit plans in Seoul Gangnam district have been analysed by construction period, and a conclusion is drawn out as following; (1) The revison of regulations in 1998 and 2005 increased livable space of 60 and 85 $m^2$ sized apartment about 16.4~20.6 $m^2$ area. (2) Bedrooms, living room, dining room and kitchen have no change in size in nominal sense, actually, they increase their size after the fact by converting balcony to livable space. (3) Bathroom, dress room and entrance space have been considerably increased in size, which is possible for available area added in place of wall footprint according to 1998 revision.