Abstract: The accelerated aging tests in mixed acid medium (H₂SO₄, HF, HCl and HNO₃ mixed solution) of glass fiber/bromide epoxy vinylester(GF/VE) composite and carbon fiber-glass fiber/bromide epoxy vinylester(CF-GF/VE) composite used in fiber reinforced plastic chimney were carried out. The changes of mass and flexural pro-perties of GF/VE and CF-GF/VE after immersing in mixed acid medium at different temperatures (25℃, 55℃, 80℃) were studied. The dynamic thermal mechanical properties and microstructures of samples were investigated to reveal the mechanism of property decline. The experimental results show that the mass gain rate of GF/VE is higher than that of CF-GF/VE when immersed under the same conditions. The diffusion activation energy of mixed acid medium in GF/VE and CF-GF/VE are 8.798 kJ·mol^-1 and 10.959 kJ·mol^-1, respectively. After 2 160 h aged at 80℃, the flexural strength retention rate of CF-GF/VE is 75.29%, but GF/VE is only 58.84%. DMA study finds that the glass transition temperature (T_g) of samples under normal immersion temperature decreases slightly, and it reduces significantly when samples are immersed at higher temperature. SEM study shows that the surface of specimen appears many micropores and its fiber/matrix interface occurs obvious debonding damage after aging in mixed acid medium.