Authors have been conducting the field research under the title ‘Origin, Transformation, Alteration and Conservation of Urban Space of Colonial cities' since 1999. This paper discusses the characteristics of the Spanish colonial cities established in Cuba focusing on San Antonio de los Baños as an irregular urban model, which has two plazas in the urban core and various types of plot division. This study has been accomplished based on the analysis of old maps from AGI (The Archive of the Indies in Seville- Archivo de Indias de Sevilla) and field survey. We clarified the original plan and transformation of San Antonio de los Baños based on the analysis of block size, block division, and plot subdivision. This paper is significant to show the Spanish Colonial city that did not follow Laws of Indies.