Vascular permeability (VP) plays a critical role in liver and kidney fibrosis progression. Traditional VP quantification methods use single-wavelength photoacoustic microscopy (PAM) with Evans Blue (EB) dye, which have limitations including signal attenuation and decreased accuracy. To overcome these issues, we developed a dual-wavelength PAM method with a spectral unmixing algorithm for quantitative VP evaluation in liver and kidney microvasculature. This approach allows for accurate assessment of VP dynamics by analyzing hemoglobin and EB absorption. Using murine models of fibrosis, we found that fibrosis reduces vessel density and increases vessel diameter, providing valuable insights into VP changes during fibrosis progression.