Abstract: The purpose of this paper is to study relative attribute reduction of set-valued decision table from the viewpoint of fuzzy rough theory.Firstly, the authors define a fuzzy tolerance relation based on the possibility of two objects having the same value in such information systems with respect to the condition attributes and give the upper approximation and lower approximation of fuzzy tolerance relation.Secondly, by introducing fuzzy approximation quality of the set-valued decision table, the paper defines the significance and relative significance of condition attributes, and proposes a heuristic algorithm for computing relative reduction.Finally, the example shows that this algorithm can obtain the relative reduction of a set-valued decision table.