This study aimed to compare and analyze the timbre of the geomungo and cello, focusing on harmonic analysis to examine the tonal characteristics of both instruments. Using pizzicato, a common playing technique for both instruments, A2, A3, and A4 notes were recorded, and the sound sources were generated using virtual instruments. By comparing the timbre of the two instruments through spectrum, spectrogram, envelope, and sound pressure analysis methods, it was found that the geomungo showed a stronger influence of harmonics than the fundamental frequency, characterized by a very fast attack and rapid release, which are key factors in forming the geomungo’s clear and bright tone. In the case of the cello, the fundamental frequency had a stronger influence than the harmonics, and it was found that the presence of subharmonics and non-harmonic partials, along with a fast attack and slow release, contribute to its deep and rich tone. This study provides an understanding of the tonal characteristics of the geomungo and cello, and it is hoped that this will contribute to the harmonious fusion of traditional Korean and Western music, as well as foster new musical diversity and creativity.