This study examined the relationship between urban form and carbon dioxide (CO2) emissions from urban area in fifty cities in Japan. The digital maps of administrative boundary were used to clip urban regions from scenes of the satellite images. The clipped images were classified into a binary class: urban built-up and others. The sectoral data for the CO2 emissions at the municipality level in 2005 were obtained from published sources. We used two types of approaches to quantify urban forms. The first method involved landscape metrics which describe compactness and complexity of settlement patches. Second method, which we developed, quantifies the reduction rate of urban area from the city center by applying ring-shaped buffers. The results indicated that there were correlations beteen spatial indices of urban form and sectoral CO2 emissions for the residential and passenger transport sectors. The inverse relationship between the compactness index and CO2 emissions in our study suggest that less fragmented and compact cities emit less CO2 from the passenger transportation sector than the sprawled cities. Our study indicates that less complex cities lower residential per capita CO2 emissions but too dense settlements in mono-centric form may lead to greater per capita CO2 emissions. Complexity seems to have less significant for CO2 emissions in general. Our research also favors a high income, smaller population size and denser city for lower CO2 emissions