The alignments of polystyrene particles of 1μm and 5μm sizes in an aqueous colloidal system were observed by varying the electric field strength, the frequency and the water flow. Spherical mono-dispersed polystyrene particles dispersed in pure water were put into a perfusion chamber; an AC electric field was applied to the Au/Cr electrodes with a 4 mm gap on the glass substrate. The mixture of the 1μm and 5μm sized polystyrene particles at 0.5 vol% concentrations for each size was set in the dielectrophoresis conditions of 1 kHz and 150 V/cm. Large particles of 5μm size were aligned to form chains as the result of the dielectrophoresis force interaction. On the contrary, small particles of 1μm size did not form chains because the dielectrophoresis force was not sufficiently large. When the electric field increased to 250 V/cm, small particles were able to form chains. After the chains were formed from both large and small particles, they began to coalescence as time passed. Owing to the electroosmotic flow of water, wave patterns along the perpendicular direction of the applied electric field appeared at the conditions of 200 Hz and 50 V/cm, when the dielectrophoresis force was small. This wave pattern also appeared for small particles at 1 kHz and 150 V/cm conditions due to the flow of solvent when water was forced to circulate.