The UASB reactor is a popular but complex anaerobic treatment mostly used to treat wastewater loaded with high organic matter. Hence, it is subjected to many complexities due to inconsistent quality and quantity of wastewater and therefore lots of uncertainties are incorporated. Thus, a fuzzy model was developed incorporating five input parameters to predict biogas production in UASBR treating distillery wastewater. A parametric sensitivity analysis of a fuzzy model has been carried out to effectively analyze the influence of input parameters on output. Effect of input parameters on the output parameter has been analyzed through scatter plots. Also, importance based ranking of various input parameters was conducted with the help of the sensitivity index. It was discovered that an increase in biogas production would be achieved if the temperature, COD reduction, COD load and alkalinity to acidity ratio is maintained as 35℃-42℃, 60,000-70,000 mg/L, 55,000-65,000 Kg/Day and 0.1-5 respectively. Moreover, the sensitivity indices of various parameters revealed that COD load and COD reduction had more importance on predicting biogas production. The results of the present study allow gaining important insights into key parameters which are responsible for affecting the performance of the UASBR under various input conditions. © 2020 WITPress. All rights reserved.