A two-stage process was developed by serial inter-connection between CSTR (Continuously Stirred Tank Reactor) and UASB (Upflow Anaerobic Sludge Bed) to produce high-rate biogas from waste textiles. Most of the textiles contain cellulose, which could be a potential substrate for biogas production. Blue jeans textile (pretreated and untreated) was used as waste textile in this process to investigate biogas production under semi-continuous conditions. Jeans was pretreated using 85% NMMO (N-Methyl-Morpholine-Oxide), an environmental friendly solvent at 120 °C for 3 h. OLR (Organic Loading Rate) was increased in the order of 2, 2.7, and 4 gVS/L/day respectively. Pretreatment had a significant effect on the biogas production. NMMO pretreatment doubled the biogas yield, during an OLR of 2 g VS/L/day compared to untreated jeans. The OLR could successfully be increased to 2.7 g VS/L/day resulted in 91% and 96% theoretical yield for untreated jeans and pretreated jeans respectively. However, further increase in OLR did not increase the methane production. For the complete process, COD (Chemical Oxygen Demand) efficiency was high for untreated jeans with 65.1% followed by treated jeans with 39.5% in the UASB. CSTR possessed the major share of biogas production for both textiles. Considering the fact that, textile is one of the largest consumer products, a proper way of disposal or treatment is necessary. By biogas production, waste textile could also be treated and a value-added product was obtained.