Sludge digestion and stabilization governs almost half of the operating cost of wastewater treatment plants, and hydrolysis is the limiting step in sludge digestion. Increasing hydrolysis by implementing pretreatment prior to digestion can increase the digestion efficiency. Among pretreatment methods, thermal pretreatment at temperatures around 160-175 degrees C tends to produce better solubilization. Microwave (MW) pretreatment was recently studied as an alternative method to conventional thermal pretreatment. Until now, MW pretreatment above boiling point had not been studied for sludge solubilization and digestion. This paper provides preliminary results on the effect of MW pretreatment operating conditions such as high temperature (T) (110-175 degrees C), MW intensity (I) (1.25 and 3.75 degrees C/min), and sludge concentration (C) (6 and 11.85%) on solubilization. From experimental results and three-factor fixed-effect analysis of variance (ANOVA) determination it was found that T, I, and C main effects and T:I and T:C interactions as well as T:I:C interaction are significant at a 94% confidence interval.