In thermal methods of oil extraction from oil shales, kerogen is converted into liquid and gaseous hydrocarbons by heating to high temperatures (usually 300 to 500 degrees Celsius). Moreover, oil extraction is accompanied by a solid residue (ash) containing minerals, heavy metals, and inorganic compounds. Ash, as a by-product, has various effects on the extraction process and the environment and plays an important role in the process of oil extraction from oil shales. Furthermore, water, as a strong absorber of microwaves, can act as a «heat carrier» in the extraction process and improve heat transfer to kerogen. In this study, the effect of ash and moisture on the characteristics of oil extracted from oil shale in heating using microwaves and the conventional method was investigated. In the microwave irradiation process, adding ash in amounts of 25 and 50 weight percent to the sample increased oil recovery. In addition, in the conventional heating process, adding ash was accompanied by an increase and decrease in oil recovery. Moreover, increasing the percentage of carbon and saturated fraction, decreasing the chain length of aliphatic compounds along with decreasing sulfur, asphaltene fraction and decreasing aromatic compounds and its entanglement index were considered as a function of improving the produced oil. The results of the percentage of carbon and sulfur components, saturated and asphaltene fractions and FT-IR, C&H-NMR spectra confirm that in microwave heating with increasing ash weight, although the amount of extracted oil shows a slight increase, the quality of the produced oil decreases. This indicates an optimal amount of ash in the extraction process that depends on its components and amount. For comparison, the experiments were repeated with conventional heating, and the results indicate that ash does not play a constructive role in improving the extracted oil in conventional heating. By adding 2.9% by weight of water to the sample, the presence of moisture in the microwave heating process was evaluated, which caused a decrease in the extracted oil. Qualitatively, the percentage of carbon and saturated fraction had a decreasing trend, sulfur and asphaltene fraction did not change significantly. The results of FT-IR and C&H_NMR spectra also indicated no improvement in the quality of the extracted oil. In conventional heating, although humidity increased the amount of oil produced, no improvement in quality was observed. Therefore, in general, humidity was not beneficial in the oil extraction process.