The effect of three different cattle dung slurry concentrations (1:1, 1:4 and 1:9) at three different HRTs of 20, 30 and 40 days was studied at pilot scale for one year. The results showed that both biogas yield and methane content of gas obtained in 1:4 and 1:9 slurry concentrations were significantly higher than those at 1:1 concentration for a given HRT. This was observed for all the three HRTs studied. At 1:1 and 1:4 slurry concentrations, methane yield was found to increase with HRT. However, at higher dilution of 1:9, increase in HRT from 30 to 40 days resulted in decrease in methane yield.