Firmness is very important factor to evaluate the freshness and ripeness among the various factors, in concerning about the melon quality. This study was carried out to develop the technique using impact signal to measure the melon firmness nondestructively. Results of analyzing impulse signals of melons having different firmness levels showed that the firmness of melon affected various impulse responses including amplitude, transmitted time, maximum peak frequency, firmness index 1 ($f^2m$), and firmness index 2 ($f^2m^{2/3}$). Impulse signal amplitude was the best indicator to predict the firmness of melon because of a strong corelation ($R^2;=;0.9071$). Firmness index 1, firmness index 2, maximum peak frequency, and normalized transmitted time were also possible indicators with acceptable correlation values.