In order to determine the working efficiency and economical size of biogas plants in respect of house hold cattle and family members, a study was carried out during 2007-08 in Chhattisgarh State, India. Fifteen blocks were selected randomly covering 117 biogas plants. Out of them, 99 plants (85 %) were found in working condition for which economic analysis was carried out. Survey results revealed that economically different sizes of biogas plants i.e. 2- 8 m³ were useful in the study area. On an average, the whole initial investment could be recovered in an about 3- 8 years. The annual income of different size of biogas plants from 2 m³, 3 m³, 4 m³, 6 m³ and 8 m³will be Rs 3620, Rs 5273.6, Rs 4215, Rs 4565 and Rs 4612, respectively. The cost of operations of different size of biogas plants (2-8 m³) were observed in the range 2.73- 4.0 Rs/h. The size of most economical biogas plant was 3 m³ (B/C= 1.23) followed by 2 m³ (B/C= 1.06).