Recently, inertial sensors have been used to measure human movements for the purpose of rehabilitation. In evaluation of motor function for rehabilitation, reference data measured from healthy subjects with inertial sensors is needed. In addition, since lower limbs perform 3-dimensional movements during gait, it is needed to analyze 3-dimensional gait movements. The plot of 3-dimensional vector locus can be useful to understand 3-dimensional movements. The purposes of this paper were to show usefulness of the vector locus in understanding circumduction during gait, and to test an evaluation parameter for 3-dimensional movements during walking as reference data. Gait of 12 healthy subjects were measured, and then vector loci were plotted in the 3-dimensional space. Shape of the vector locus was evaluated by the width of each component as one of the reference data. It was suggested that the vector loci plotted in 3-dimensioinal space or those projected on horizontal plane were useful to understand circumduction during gait. It was also suggested that the width of vector locus was useful to evaluate differences of movement between subjects.