Purpose: Evaluation of antifungal activity and inhibiting effects of the Kabikaj herb on the most important destructive fungi of paper material such as Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Penicillium spp. and Cladosporium spp.Design/Methodology. Findings were determined by mixing aqueous and hydro-alcoholic extracts with Sabouraud dextrose agar. To assess the inhibitory effects of extracts on fungi on paper, aged filter papers were used as samples in three groups: control and two test samples were inoculated with the aqueous extract and hydro-alcoholic extract. All samples were inoculated with the prepared suspensions of spores and the effects of plant extracts on the structure of the paper was investigated by tests such as determination of acidity, colorimetric investigations, tensile strength tests and ATR-FTIR.Findings: Kabikaj herb has a noticeable effect on controlling the growth of fungi. In samples impregnated by aqueous extract in the ratio of 1:20 and samples impregnated by hydro-alcoholic extract in the ratio of 1:180, the plant extract inhibited the all five types of the fungi growth. The highest sensitivity against extracts was observed in Penicillium spp. and Cladosporium spp. in which the inhibitory percentage of Hydro-alcoholic extract in ratio of 1:200 was 99.57% for Penicillium spp., and was 99.87% for Cladosporium spp.. After aging, the paper samples treated with both extracts were reduced to 4.0 units in pH level. According to colorimetric results, by increasing the b* factor (yellow/blue) the intensity of yellowing process, and decreasing L* factor (brightness/darkness) the darkening process increased. After the aging process, in samples treated by aqueous extract, about 0.46 unit and hydro-alcoholic extract about 0.41 unit reduction in tensile strength was observed. Generally the hydro-alcoholic extract in comparison to aqueous extract showed more appropriate inhibitory power against fungi, and also its color affects and tensile strength reduction is minor.