The evaluation of density and micro-void defects of epsilon-HNIW crystals was investigated in the drowning-out crystallization. Also, methods to quantitatively evaluate the crystal void defects were developed by using pycnometer and differential scanning calorimeter. Since the epsilon-HNIW crystals were re-constructively transformed from beta-HNIW, which was crystallized out by drowning-out crystallization, the density and defect of epsilon-HNIW crystals were predominantly determined by the growth process during the phase transformation. Due to contradictory contributions of crystallization conditions on crystal defects, the crystal density was maximized at around the anti-solvent feeding time of 120 min and temperature of 25 degrees C within ranges of the anti-solvent feeding time and temperature from 0-180 min and 5-30 degrees C, respectively. Based on comparison of the measured crystal density with ideal one (2.044 g/cm(3)), the void defects of crystals were estimated. In addition, the thermal energies related with the solid-state phase transition from epsilon-HNIW to gamma-HNIW and decomposition of HNIW were indicated to successful quantification of crystal defects owing to the significant changes of the thermal energies with the crystal density. Using the X-ray microscopic analysis with 80 nm resolution, it was proven that the micro-void defects in the crystal existed obviously to cause the change of crystal density and thermal properties.