Ferrous fumarate was microencapsulated by the ethylcellulose coacervation process which is based on the differential thermal solubility in cyclohexane. The effects of butyl rubber (isobutylene-isoprene copolymer) and Adsolider 101 (SiO₂) on the preparation of microcapsules were studied. When a protective colloid, butyl rubber, was present in adequate concentration, individually film coated core particles formed. In the absence of butyl rubber, the final product was in the form of large aggregates, in contrast to individually microcapsulated particles. And addition of anticoagulant, Adsolider 101, reduced the amount of aggregated mass of final product. When Adsolides 101 was used in 3% ratio to the weight of core material, the aggregated mass (remaining on the No. 50 sieve) of final product was about 1%. The particle size distribution of microcapsule which was treated with Adsolider101 was more homogenous than that of untreated microcapsule.