Abstract: This paper presents the separation experiments and results by a A3-1 continuous free-flow electrophoresis device on board the Russian weightless aircraft. The A3-1 device consists of power conditioning unit, detection unit and electrophoresis unit. The power conditioning unit converts 27V DC coming from the bus into the power sources required for electrophoresis unit. The detection unit has a video tape recorder used for recording the separation picture and a single chip which control the power supply, the detecting, record and storage of operating data. The electrophoresis unit is a electrophoresis separation system in which the rectangular separation chamber has the following internal dimensions: 270 mm long, 60 mm wide, and 3 mm thick （gap）. During operation of A3-1 device, the separation process is monitored with a CCD head placed the front of separation chamber and recorded in the video tape recorder （Video Hi8） in the detection unit. The carrier buffer （the electrode buffer is the same）, used for all experiments, contains 3.5 mMol TEA （Triethanolamine）, 0.7 mMol NaAc and 10% glycerol. The sample to be separated is a kind of mixture containing two colored model proteins, Hemoglobin （HB, yellow） and Cytochrome c （red）. The flight test was performed for tour times. For each flight the aircraft would conduct 10-12 parabolic flights and lasted nearly one hour. The pictures of elec-trophoretic separation and the experimental data were obtained. The results showed that the A3-1 CFFE device worked well and the effect of gravity change on the elec-trophoretic separation process of biological samples can be seen clearly from the pictures. The shape of sample filament is different under different flight state. The filament under the horizontal flight （near 1 g） appears spread and bent to the right near the outlet. The filament under the overweight （1-2 g） flight is not clear due to serious spread, the separation of sample was bad. But the filament under the micro-gravity （0-0.4 g） condition is quite clear （less spread） and almost in a straight line. It was shown that the microgravity environment is beneficial to the electrophoresis separation of biological material.