Abstract: Fussy set theory provides a simple framework for integrating and analyzing qualitative and quantitative data irrespective of their sources. This study introduces fussy logic and demonstrated its application for predicting hydrothermal mineral occurrences in northwestern part of Yunnan. Three geo-variables were considered and their membership functions were determined subjectively. Combination of the three fussy evidence layers; geochemical, lineament and lithology resulted into a favorability map for the occurrences of hydrothermal Cu, Ag, Au and Pb-Zn.