A new method for pptn. of micro-sized solid particles in the riser of an agitated internal-loop reactor was developed. The solid CaCO3 particles were pptd. inside of drops of aqueous CaCl2 and Na2CO3 solutions which played role of micro-reactors with dispersed (mixed emulsion) phases. The solid particle size (Sauter diameter) increased from 1.2 to 5.9 mu m with the decreasing surfactant concn. and the increasing concn. of the substrates. The largest particles were obtained when the rotational speed of the propeller was 40 s(-1). The particle residence time did not influence the CaCO3 particle size. Solid particles obtained in the emulsion system were distinctly smaller than those obtained as a result of the pptn. in the 2 mixed aqueous solutions in the same reactor.