Four novel antimicrobial maleimido phenyl thiourea derivatives were synthesized from N-[4-(chlorocarbonyl) phenyl] maleimide with phenyl thiourea and its derivatives (p-methyl, o-chloro, and p-carboxy). Their structures were characterized by FTIR, H-1 NMR, mass spectra, and elemental analyses. Their antimicrobial activities against three types of bacteria (Bacillus subtilis, Streptococcus pneumoniae, and Escherichia coli) and against three crop-threatening pathogenic fungi (Aspergillus fumigatus, Geotricum candidum, and Syncephalastrum racemosum) were investigated. The results revealed that these derivatives are effective in inhibiting the growth of the tested bacteria and fungi as indicated from the inhibition zone diameter and minimum inhibitory concentration. The antibacterial activities of these derivatives were more effective against Gram-positive bacteria than Gram-negative bacteria. These derivatives were investigated as thermal stabilizers for rigid poly(vinyl chloride) at 180 degrees C in air by measuring the rate of dehydrochlorination and the extent of discoloration. The results reveal the greater stabilizing efficiency of the investigated derivatives as shown by their longer thermal stability periods (Ts) and lower dehydrochlorination rates in relation to dibasic lead carbonate, cadmium-barium-zinc stearate, and n-octyltin mercaptide industrial stabilizers. The stabilizing efficiency increases with the introduction of electron-donating substituent groups in the aromatic ring of the stabilizer molecules. Moreover, the investigated stabilizers impart better color stability for the degraded samples as compared with the reference stabilizers.