OBJECTIVE:To prepare Activated carbon N-acetylcysteine microcapsule (ACNAC),and to optimize preparation technology. METHODS:ACNAC was prepared by emulsion cross-linked method using biodegradable material gelatin as capsule wall material. Using comprehensive evaluation index of drug-loading amount,entrapment rate and particle size distribution percent-age(the percentage of 80-140 μm particle)as index,drug-loading ratio,amount of gelatin,mixing speed and the amount of emul-sifier as factors,single factor test and orthogonal test were used to optimize formulation technology. The technology was validated and distribution of particle size of ACNAC was determined. RESULTS:The optimal formulation technology was as follows as drug-loading ratio 1∶1,gelatin 15%,emulsifier 2.0%,mixing speed 1 000 r/min. Average drug-loading amount of 6 batches of ACNAC was 15.9%(RSD=1.21%),average encapsulation efficiency was 78.1%(RSD=1.11%)and average particle size distri-bution percentage was 81.9%. CONCLUSIONS:ACNAC is prepared successfully,and formulation technology is reasonable and feasible.