The influences of a surrounding sphere of different size, located at various distances and angles, on the drag and the flow characteristics of a test sphere have been experimentally investigated. The liquid viscosity is increased in an effort to enlarge the magnitudes of drag to a measurable range. The drags of an interactive particle can then be actually determined by the help of a:precise electronic balance. Flow-field measurements are conducted using a non-intrusive LDA system. The refractive index matching technique is applied to overcome the optical difficulty caused by the passage of a laser beam through a curve surface. Empirical correlations are developed to calculate both the form and the friction drags of an interactive particle. Flow properties under different interactive conditions are closely related.