A major problem facing municipalities of Bahir Dar city is the treatment, disposal and/or recycling of faecal sludge and solid wastes. Now a day in the city, there are some methods being used to treat and dispose faecal sludge and solid wastes to the landfill and reuse it after composting. Although there are many methods available, selection of efficient and environmentally safe method for the local condition requires detail study. The use of effective microorganisms (EM) is one of the latest organic waste treatment technologies to reuse and safely dispose the waste to the environmental. This study aims to assess the effect of EM addition and mix ratio of organic solid waste and faecal sludge in pit and heap composting methods. There are seven pits and three heaps treatments in this study, in which six pits, two heaps were tested with EM, one pit, and one heap were tested without EM as a control. Each treatment was allowed to decomposefor40 days of composting duration. Temperature, pH, total nitrogen, total phosphorous, potassium, sodium, calcium, magnesium, organic carbon, electric conductivity, moisture content, ash content and C/N ratio were measured to evaluate the level of decomposition of organic wastes and faecal sludge within 40 days. Based on the results of 40 days composting, the overall temperature ranges from 25 ˚C to 29 ˚C. On the other hand, during the period of composting, the pH value in pit and heap composting as well as with EM based and without EM in each treatment is from 6 to 8. This shown that the microbial respiration in the composting pit and heap was inhibited and had approached the mature phase. As for NPK content, total Nitrogen value range from 0.15% to 2.11% for pit composts, while 0.25% to 0.47% for heap composts. Total Phosphorus has the values of 0.12% to 0.76% for pit composts and 0.05% to 0.09% for heap composts. On the other hand, result for potassium is from 4.99 cmol/kg to 35.69 cmol/kg for pit composts and from 10.95 cmol/kg to 14.05 cmol/kg for heap composts. Result showed that the good mixing ratio of organic solid waste to faecal sludge is 0.65m3 to 0.35 m3 in volume and with 2 liter activated effective microorganism per a cubic meter mix. Generally, this study conclude that pit composting method were found effective than heap composting as well as pit composting with addition of EM is efficient method than pit composting without the addition EM to matured compost.