The dielectric response of cellulose in the form of paper and pressboard was investigated. Samples of pressboard were impregnated with different insulating liquids: new and aged transformer oil and synthetic ester. Samples of non-impregnated paper were investigated during drying process. The research was done for two groups of pressboard with about 5 % and 0.5 % moisture content. The moisture level was determined using Karl Fischer titration. Obtained data were analyzed using Havriliak-Negami relaxation function. The results can be useful for moisture evaluation in various impregnated cellulose insulations e.g. transformers, bushings, capacitors.