This study aimed to develop a seasoning using onion soy sauce powder. The results from the evaluation of general components showed that the sample with 30% onion soy sauce powder had the highest value. As the content of onion soy sauce powder increased, the pH decreased and the titratable acidity increased. Regarding chromaticity, the L value decreased, and the a and b values increased with increasing content of onion soy sauce powder. The free sugar and quercetin content increased as the amount of onion soy sauce powder increased. The total polyphenols, total flavonoid contents, and DPPH, ABTS, and SOD activity increased as the powder content of onion soy sauce increased. The sensory evaluation results showed that 20% onion soy sauce powder was the most preferred overall, but the difference was not statistically significant.