The localization of sensor nodes is one of the key issues for sensor network systems. Therefore, to obtain precise location information, several localization systems have been researched. However, they need an arranged space using a large number of anchor nodes whose locations are well known, or they need advance information such as information on radio conditions in the space. If not, then the systems cannot be used for a space that cannot be arranged in advance with suitable conditions for these systems' operation. Furthermore, some localizations assume the use of advanced distance measurements, such as TOA and TDOA, to achieve high accuracy in estimating locations, but these advanced distance measurement schemes cannot be used for ordinary sensor node systems. To resolve these problems, we propose node localization based on Self-Organizing Maps for wireless sensor networks. The proposed localization uses RSSI based distance measurement, which can be used for ordinary sensor node systems. The proposed localization reproduces a geometry similar to the network's original geometry without anchor nodes, and it reproduces a geometry with two anchor nodes that is congruent with the original. Furthermore using just three anchor nodes, it estimates node absolute localization with high accuracy. In this paper, the algorithm of Self-Organizing Localization is described, and its characteristics based on simulation evaluation are shown.