In this study, we have conducted earthquake monitoring on a timber Buddhist temple constructed in 1825. Between 2008 and 2019, 75 strong motion were recorded. The maximum response acceleration was recorded during the 2011 Tohoku earthquake, Japan. From the long-time monitoring, the influence by time due to deterioration and exterior force was expected, but the natural frequency of vibration/stiffness did not show any fluctuation in our 12 years of measurement. There was a strong correlation with the natural logarithm of the maximum relative displacement, reflecting the non-linear elastic characteristics of timber structures. However, the natural frequencies of vibration were 10-20% higher in the summer than in the winter, when the climate was hot and humid. The effect of moisture content on the mechanical properties of wood was also investigated and an idealized relationship between the maximum relative displacement and the normalized natural frequency of vibration by MC was proposed.