Photothermal materials (PTMs) have been intensively investigated in the fields of photothermal conversion. Superior to solid PTMs, liquid PTMs are leading the trends in satisfying the demands on high flexibility and easy recycling. Successful examples of liquid PTMs that are mostly formulated by dispersing solid PTMs in solvents bear on the problems of phase segregation and solvent pollution. In this work, we proposed a low-cost formulation which refers to an oxidative product of ethyl oleate by iodine. It is an intrinsic liquid PTM, preserving the fluidic nature as well as possessing considerable ability of photothermal conversion. In addition to understanding the mechanism of light absorption in visible and even near infrared windows, two examples were presented to demonstrate the great potentials of liquid PTMs in broad areas such as light sensing and energy storage.