To know the existance and structure and function of mitochondrial membrane aldehyde dehydrogenase (ALDH) as a final goal, mitochondrial membrane from rat liver was purified using sucrose step gradient (1∼2 M) centrifugation, and then sonicated and ultracentrifuged to obtain pure mitochondrial membrane fraction. The observation of the ALDH activity from this fraction let us know the existance of mitochondrial membrane ALDH. The result that various kinds of detergent (Triton X-100, Digitonin, Lubrol PX, Cholate and Chaps) were examined as a good solubilizer at several different concentrations showed 1% cholate for the best one. In addition to this, the optimum salt (NaCl) concentration and pH for solubilization were 1 M and 9.0, separately. And also, the addition of phospholipid functioned as a stabilizer. The partial purification of ALDH from this cholate-solubilized membrane fraction with selected best conditions was tried using sucrose linear gradient (3∼10%, including 1% cholate and 5 ㎎/㎖ phospholipid) centrifugation and was obtained more 100 times than crude mitochondrial state as a result. This partial purified, cholate-solubilized ALDH was dialyzed to remove the cholate and to make ALDH-incorporated vesicles. ALDH activity from this result was increased about 2 times than before dialysis.