Tomato (Solanum lycopersicum) is an important crop in the Solanaceae family. One of the key traits selected during domestication is fruit mass which is controlled by many quantitative trait loci. The fruit weight locus fw3.2 is one of the major loci responsible for fruit mass in tomato. Identification of the underlying gene will improve our understanding of the molecular mechanism of fruit development while also providing insights into genes that were selected during domestication. We fine mapped fw3.2 to a 51.4-kb interval corresponding to a region comprising seven candidate genes. Gene action showed that the allele from cultivated tomato was additive to dominant in giving rise to an enlarged fruit. Fruit shape analysis indicated that fw3.2 primarily played a role in controlling fruit weight, with a minor effect on fruit shape. Gene expression and nucleotide diversity were investigated and the likelihood of the genes control fruit mass is discussed.