New biologically active polyurethane composites were prepared by surface modification of polyurethane foams with thiourea and benzaldehyde. The current work introduces an efficient antimicrobial composite of thiourea polyurethane foam/benzaldehyde (TPU/Benzaldehyde). The main techniques used for thiourea polyurethane foam/benzaldehyde composites identification were Infrared spectra, Ultraviolet-Visible spectra, bandgap energy, X-ray diffraction, Scanning electron microscopy, magnetic susceptibility, and pH of zero-point charge (PHZPC). Surface functions such as carboxylic, lactonic, and phenolic hydroxyl groups have been identified via Boehm titration. The chemical stability of TPU/Benzaldehyde was tested in diverse buffer solutions (pH: 2–14) and various organic solvents (e.g., CH3OH, CH3COCH3, C6H6, C6H5CH3, DMF, and DMSO). The weights of TPU/Benzaldehyde were unaffected, which confirm its chemical stability. TPU/Benzaldehyde was tested for antibacterial and antifungal activity against Gram-negative bacterium E. coli, Gram-positive bacterium B. cereus, and fungus A. niger. TPU/Benzaldehyde had higher inhibition zones against Gram-positive B. cereus than Gram-negative E. coli, with inhibition zones of 18±0.03 and 16±0.03 mm, respectively. Also, TPU/Benzaldehyde had higher antifungal action against A. niger, with inhibition zones of 20±0.24 mm, than the standard antifungal agent, Fluconazole (14±0.14 mm).