The particleboards made with ammonium chloride had the highest flexural properties, followed by the particleboards made with ammonium sulphate and ammonium chloride, respectively. The flexural properties of the particleboards containing urea were slightly lower than those of the particleboards containing urea (Table 4). The MOR and MOE values of one month conditioned particleboards were higher than those of one day conditioned particleboards. For example, the MOR and MOE values of one day conditioned particleboards made with ammonium chloride and without urea were 13.74 N/mm2 and 2283.8 N/mm2 while they were found as 14.59 N/mm2 and 2458.6 N/mm2 for the same particleboards after one month conditioning period. The hardener type and conditioning period significantly affected the MOR and MOE while the urea usage did not affect them according to the results of Newman–Keuls test. Significant differences (p < 0.05) between group averages for the MOR and MOE values are presented in Table 6 as letters. Based on the EN 312 [18] standard, 11.5 and 13.0 N/mm2 are the minimum requirements for MOR of particleboards for general uses and interior fitments (including furniture), respectively, while the minimum requirement for MOE of particleboards for interior fitments is 1600 N/mm2. All of the particleboard types, except for types 5 and 6, had higher MOR for general purposes. Particleboard types 1, 2, and 7–10 had the required levels of MOR and MOE for furniture manufacturing.