Excess sludge from municipal wastewater treatment plants (WWTP) take approximately up to 60% of total cost of plant in order to management, dewatering, traort and disposal. Anaerobic digestion present in most of WWTP is usually used for stabilization of sludge before disposal. Considerable research has been conducted to enhance the proficiency, accelerating conversion process and reducing the excess sludge volume in processes of producing biogas as a renewable energy source from urban wastewater treatment plant sludge. Excess sludge from wastewater treatment plant which is an environmental pollutant contains high quantity of organic compounds (COD about 60000 mg/L) for producing biogas. Excess sludge of urban wastewater treatment plant contains high quantity of microbial cells with rigid wall which prevents microorganisms from reaching the organic containments inside the cells which in turn reduces the biogas production efficiency and elongates the anaerobic fermentation. Various biological, chemical and physical procedures have been used for breaking these cells and to accelerate this stage of fermentation. In this project two types of feed, including secondary sludge and mixed sludge (a mixture of initial and secondary sludge), were used. In first set of experiments, basic, ultrasonic and microwave pretreatment at ambient temperature (20 °C) and 40 °C were done in case of mixed sludge to enhance the biogas production and reduce the excess sludge volume. In second set of experiments, chemical pretreatment with H 2 O 2 and basic pretreatment with NaOH and KOH as well as acidic pretreatment with HCl were used on secondary sludge at ambient temperature (20 °C). First set of experiment in which a comparison between basic, microwave and ultrasonic pretreatment of mixed sludge at ambient and medium temperature was performed showed that the highest efficiency belongs to the basic pretreatment, pH=12 and 20 °C, and 365 mL biogas/gr COD was obtained which shows a 242 % increase in comparison with untreated sample. After that the highest efficiency belonged to the sample at condition of 40 °C and pH=12, and obtained result equals to 352 mL biogas/gr COD. Increase of methane containment in produced biogas from 50% obtained from raw sludge to the 72% from ultrasonic pretreated sample at 20 °C shows the biogas quality development. In case of the second set of experiment on the secondary sludge a comparison between different chemical pretreatment methods at ambient temperature (20 °C) was performed, and the highest biogas production enhancement in comparison with untreated sample belonged to the sample which was pretreated by KOH and it was 72%. After that the sample pretreated by H 2 O 2 at concentration of 2400 mg H 2 O 2 /L with 69% efficiency had the highest efficiency. The highest rate of methane containment increase in biogas was obtained through the sample pretreated by H 2 O 2 at concentration of 2400 mg H 2 O 2 /L and it was 64%. Key words: Biogas, anaerobic digestion, excess sludge, microbial cells, pretreatment