This thesis discusses the effectiveness of division Area Regency in West Kalimantan Province. From the research result using normative and sociological law research method. From the results of the analysis and discussion to get the conclusion that is: Pemekaran Daerah In West Kalimantan Province The legal basis for the establishment of new autonomous regions using Law No. 22 of 1999 on local government and Government Regulation No. 129 of 2000 on the requirements of the formation and criteria of pemekaran, deletion and merger of regions , In 2004 was revised into Law Number 32 Year 2004 and Government Regulation Number 78 Year 2007 and revised back into Law Number 23 Year 2014, Law Number 9 Year 2015 regarding the second amendment to Law Number 32 Year 2004 On Regional Government but the Government Regulation on Regional Arrangement and the great design of regional arrangement is still discussed by the Ministry of Home Affairs and has not been published until now. Implementation of Regional Expansion District In West Kalimantan Province Runs Effectively To Achieve People's Welfare. The main concern of the government at this time is that the number of areas that after the split did not provide the level of welfare to the people, even worse than before it was split, such as West Kalimantan. In some cases, the phenomenon of regional pemekaran tends to shift into a tool for sharing power for political purposes, which is very contradictory with the purpose of regional expansion, namely for the welfare of society. Expansion of the territory is of national interest intended to provide benefits to various groups, both society and government, because the expansion of the region will make the area, become open, the development path is wider, scattered, and productive. In addition, the urgent factor in the expansion of a region is to avoid the concentration of development from various sectors of life in the area that is allegedly competent, thus the need for the expansion of the region encourages its fulfillment by separation from the parent government, with the main objective of accelerating the welfare of the people.