Abstract: For genetic algorithms based path planning of a mobile robot,a novel fixed-length decimal encoding mechanism for the paths of the mobile robot is proposed in this paper. First of all,the obstacles in the robot environment are described as polygons. Then,the vertexes of all polygons are numbered in decimal. The paths are then encoded into decimal chromosomes of fixed length,which equal the amount of all vertexes. In such a chromosome,each nonzero bit is the decimal number of a vertex the path passes. The order of vertexes in a chromosome is that in a path. Such an encoding mechanism overcomes the shortcomings of variable-length encoding mechanism and other fixed-length binary encoding mechanisms where special decoding and genetic operators are needed,resulting in simplicity and effectiveness of the algorithm.