In this paper, an experimental study was conducted to examine the influence of cyclic hygrothermal conditioning on the interfacial properties of CCF300 carbon fiber/BMI composites.The specimens were initially immersed in distilled water at 71 ℃ for 14 days until moisture saturated proximately, which were placed to an oven at 85℃ to obtain constant weight later after.Repeating the water absorption-desorption cycle for three times, it was found that the re-absorption stages often exhibit higher diffusivity and higher saturation level.This could be linked to the irreversible damage induced by absorbed moisture, which could be confirmed by SEM images of fracture surface of relevant composite specimens.