This study aimed to investigate and optimize the quality of tomato 'Soksungjang'. Tomato 'Soksungjang' was prepared using 10% tomato paste with the addition of Rhizopus oligosporus Koji. Various quality characteristics were determined including proximate composition, physicochemical properties, free sugar and organic acid contents, free amino acid content, total microbial count, enzyme activity, and the presence of volatile compounds. The results showed that the free sugar content of tomato 'Soksungjang' was 14.81 mg%. The individual sugars identified were glucose, galactose, fructose, sucrose, maltose, and lactose. The total organic acid content was 162.79 mg% and the identified individual organic acids were citric acid, lactic acid, acetic acid, malic acid, formic acid, and succinic acid. The total free amino acid content was 1,440 mg%, including major amino acids, such as glutamic acid, lysine, and arginine. The α-amylase activity of the tomato 'Soksungjang' was 74.42 unit/mL, whereas lipase and neutral protease activities were 93.59 and 35.79 unit/mL, respectively. Total 30 compounds including alcohols, esters, ketones, and aldehydes were detected in tomato 'Soksungjang'. Ethyl alcohol, 3-methyl-1-butanol, and ethyl acetate were among the major volatile compounds.