This study aimed (1) to understand the physicochemical characteristics of the substrate by-product of oak bark and two hydroponic substrates, perlite and coir dust, at different mixing ratios, and (2) to use this by-product as a tomato hydroponic cultivation substrate. The mixing ratios of perlite and coir dust to the by-product of oak bark on a volume basis were 10:20:70 (PCO127), 30:20:50 (PCO325), 50:20:30 (PCO523), 20:10:70 (PCO217), 20:30:50 (PCO235), and 20:70:10 (PCO271) using commercially available coir slab (dust:chip = 50:50(v/v)) as a control substrate. The particle size increased to 2.8–5.6 ㎜ as the ratio of perlite was increased; however, there was also a decrease in the range of 355 ㎛–1.4 ㎜. The distribution of diameters with lengths of 5.6 ㎜ or greater decreased as the coir dust ratio was increased and the oak bark by-product ratio was decreased, but the 2.8–5.6 ㎜ diameter range increased. The bulk density was highest in PCO217 (0.22 ㎎·m<sup>-3</sup>) mixed with oak bark and lowest in the control (0.12 ㎎·m<sup>-3</sup>). The particle density was higher in PCO253 (1.22 ㎎·m<sup>-3</sup>) and PCO127 (1.21 ㎎·m<sup>-3</sup>), both of which had a higher ratio of coir dust and oak bark by-products, compared to, the other substrates, and the lowest was 0.69 ㎎·m<sup>-3</sup> in the control. For PCO325 and PCO523, the corresponding outcomes were 0.97 ㎎·m<sup>-3</sup> and 0.95 ㎎·m<sup>-3</sup>, indicating that the particle density decreased as the content of perlite was increased. The bulk density was in the 80% range in the PCO127 and control cases, and the air space was in the proper range of 22.9–26.2% on all substrates except for the control and PCO253 cases. The container capacity exceeded 60% in the control, PCO127, and PCO253, specimens and was within the proper range. As a result of analyzing the pH, EC, and inorganic elements of the substrates, the pH was found to increase while EC, P₂O₅, and NH4-N tended to decrease as the perlite contents were increased and as the amounts of oak bark by-products were decreased. Conversely, as the content of coir dust increased and the mixing ratio of the oak bark by-products decreased, EC, P₂O₅, and NH₄-N tended to increase. Additionally, NO₃-N within the culture substrate decreased as the oak bark by-product ratio was decreased. Exchangeable cations (K, Ca, Na, Mg) remained unaffected by inorganic perlite. The K and Na contents increased as the coir dust ratio was increased. However, the Ca content decreased as the oak bark by-product ratio was decreased. As a result of comparing tomato growth characteristics, except for the leaf number, there were no statistically significant differences found among the plant heights, stem diameter Ⅰ outcomes (from 1 cm apart from the base), stem diameter Ⅱ outcomes (stem lower at the last flower cluster from the apical zone), the leaf and stem fresh weights and the dry weights by substrates. The fruit yield and weight were highest at 17.6 units and 3,996 g, respectively, in PCO253. The water supply for producing 200 g of fruit was lowest at 8.3 L in T4.