We observed stable nanobubbles both in bulk ultra-pure water and at Si-water interface using scanning confocal laser microscope. Since the thermal properties of nanobubble liquid are unknown so far, the specific heat capacity of nanobubble liquid is measured using the differential scanning calorimetry. We found that the heating rate, the mass of sample and the reference are important to obtain the accurate specific heat capacity of liquid. As a result, the specific heat of nanobubble liquid is obtained, showing lower value than that of the base liquid without nanobubble.