A method for preparing microparticles comprising finasteride, the method comprising: 1) preparing a first mixture by dissolving a biodegradable polymer and finasteride in an organic solvent; 2) preparing a second mixture by dissolving a surfactant in water; 3) infusing the first mixture in Step 1) into a microchannel in a straight-line direction and allowing the first mixture to flow; 4) preparing microparticles in a form in which the finasteride drug is uniformly distributed in spherical biodegradable polymer particles by infusing the second mixture in Step 2) into a microchannel formed on both side surfaces or one side surface and allowing the second mixture to flow so as to form an intersection point with a microchannel through which the first mixture in Step 3) flows in a straight-line direction, and intersecting a flow of the first mixture in a straight-line direction with a flow of the second mixture; 5) collecting the microparticles produced at the intersection point in Step 4); 6) evaporating and removing an organic solvent present in the microparticles collected in Step 5) by stirring the microparticles; and 7) washing the microparticles in Step 6) and drying the microparticles, wherein the microparticles have an average particle diameter of 20 to 70 μm, as derived from the width and the height of a cross-section of the microchannels, which are both within a ratio range of 0.7 to 1.3 for the average diameter of the microparticles, wherein Step 6) comprises: Step 6-1) firstly stirring the microparticles at a rate of 800 to 1,200 rpm at 14 to 16°C for 1 to 2 hours; Step 6-2) secondly stirring the microparticles at a rate of 800 to 1,200 rpm at 19 to 21°C for 0.5 to 1.5 hours after the first stirring; and Step 6-3) thirdly stirring the microparticles at a rate of 800 to 1,200 rpm at 24 to 26°C for 0.5 to 1.5 hours after the second stirring. 1) preparing a first mixture by dissolving a biodegradable polymer and finasteride in an organic solvent; 2) preparing a second mixture by dissolving a surfactant in water; 3) infusing the first mixture in Step 1) into a microchannel in a straight-line direction and allowing the first mixture to flow; 4) preparing microparticles in a form in which the finasteride drug is uniformly distributed in spherical biodegradable polymer particles by infusing the second mixture in Step 2) into a microchannel formed on both side surfaces or one side surface and allowing the second mixture to flow so as to form an intersection point with a microchannel through which the first mixture in Step 3) flows in a straight-line direction, and intersecting a flow of the first mixture in a straight-line direction with a flow of the second mixture; 5) collecting the microparticles produced at the intersection point in Step 4); 6) evaporating and removing an organic solvent present in the microparticles collected in Step 5) by stirring the microparticles; and 7) washing the microparticles in Step 6) and drying the microparticles, Step 6-1) firstly stirring the microparticles at a rate of 800 to 1,200 rpm at 14 to 16°C for 1 to 2 hours; Step 6-2) secondly stirring the microparticles at a rate of 800 to 1,200 rpm at 19 to 21°C for 0.5 to 1.5 hours after the first stirring; and Step 6-3) thirdly stirring the microparticles at a rate of 800 to 1,200 rpm at 24 to 26°C for 0.5 to 1.5 hours after the second stirring.