The external ear generates resonance gain because of anatomical characteristics. The ear canal resonance is influenced by the length and volume of the ear canal, the pinna, the concha cavity, the body trunk, and the speed of sound wave. This study is focus on the influence of the volume of ear canal. 17-healthy-adult (32 ears) were participated. They did not have any medical and ear disease history. The maximum resonance frequency of the ear canal was 2675 (${pm}265$) Hz at azimuth $0^{circ}$ and 2784 (${pm}268$) Hz at azimuth $45^{circ}$. The resonance gain was 18.1 (${pm}3.9$) dB at azimuth $0^{circ}$ and 17.9 (${pm}3.8$) dB at azimuth $45^{circ}$, respectively. The ear canal volume was 0.78 (${pm}0.2$) cc and 1.32 (${pm}0.8$) cc including static compliance. The ear canal resonance was changed depending on the ear canal volume. It was also statistically correlated at azimuth $0^{circ}$ (p=0.038) and $45^{circ}$ (p=0.013), respectively. The resonance gain was not correlated with the ear canal volume. The change of resonance frequency according to the ear canal volume will be useful information in the field of audiological rehabilitation especially for hearing aids fitting. In addition, we expected this study can provide the basic information for the study of the external ear resonance characteristics.