Disclosed herein is a method for producing microparticles of an active ingredient via an in-line recirculating mixing system, wherein the in-line recirculating mixing system comprises a mixer and a conduit couple to the mixer. The method disclosed herein comprises the steps of: (a) forming a continuous phase of a medium in the in-line recirculating mixing system； (b) allowing the continuous phase of the medium of the step (a) to come into contact with a first mixture of the active ingredient, a polymer and a solvent at a site in the conduit, thereby forming a second mixture, in the conduit； and (c) allowing the second mixture of the step (b) to enter the mixer and circulate in the in-line recirculating mixing system until the microparticles of the active ingredient are formed.在此揭示一種利用連續式循環混合系統製備活性成分微粒的方法，其中所述連續式循環混合系統包含一攪拌機及與所述攪拌機耦接的管路。在此所揭示的方法包含以下步驟：(a)於連續式循環混合系統內形成一介質之一連續相；(b)將步驟(a)之該介質之連續相於該管路內的一處接觸一第一混合物，以於該管路內形成一第二混合物，其中第一混合物由所述活性成分、一聚合物和一溶劑所組成；以及步驟(c)讓步驟(b)中的第二混合物進入攪拌機中，且於連續式循環混合系統內循環，直至形成所述活性成分微粒。
