Mixing experiments were conducted by performing image analysis of tracer particles for double-blade kneader mixers with various types of mixing vessels and blades. A method of assessing the processes of macro-and micro-mixing for wet particle systems was established, and this method was applied to the assessment of mixing performance of double-blade kneader mixers. The relationship between the shapes of R(r) curves that represent the degree of mixing proposed by Danck-werts and aspect ratios of segregations were investigate, where R(r) is the correlation coefficient used to calculate the scale of segregation for the two measured points of separated by the distance r. The difference of degree of mixing between actual and ideal R(r) curves was defined as the distortion degree of mixing. For these analyses, we developed a procedure for analyzing the measured images of mixing processes of wet particles accompanied with tracer particles of almost the same sizes as wet particle sizes at an appropriate magnification corresponding to the state of micro-mixing at particle-size level. As a result, it was shown that micro-mixing could be assessed through detailed investigation of particle mixing processes in which the scale of segregation decreases and the aspect ratios of segregation approach the specific value of particle.