This study was carried out to evaluate the antimicrobial and clinical efficacy of MTAD versus Propolis irrigation of necrotic primary molars and to compare their efficacy on smear layer removal in root canals of primary teeth. This study was divided into 2 parts; part (A) was in vivo and part (B) was in vitro, A) Vivo study The sample on which this part of the study was conducted consisted of 100 non vital mandibular primary molars with necrotic pulps indicated for pulpectomy, among 100 healthy cooperative children. The children age ranged from 4 years to 6 years. They were randomly selected from the outpatient clinic of Pediatric Dentistry Department of Faculty of Oral and Dental Medicine, Cairo University. Patients were randomly divided into 2 groups, where in group A, MTAD was used for irrigation of the root canals during pulpectomy, while in group B, Propolis was used for irrigation. - Selection Criteria Patients included in the current study were selected according to the following criteria: 1- Presence of clinical signs or symptoms suggesting a non-vital tooth, such as localized swelling, sinus, tenderness on percussion or slight mobility. 2- Periapical radiograph showing periapical or furcational radiolucency. 3- Restorable tooth. 4- Patient and parent cooperation. Exclusion Criteria: - Non-restorable tooth - Uncooperative patient. - Presence of advanced physiologic or pathologic root resorption. - Presence of any systemic disease which would contraindicate pulp therapy. Pulpectomy was performed following the guidelines of pulp therapy for primary teeth by the American Academy of Pediatric Dentistry. Canals were irrigated using either MTAD or propolis irrigation. Microbiological samples were collected from the root canals before and after irrigation and 48 hours after irrigation, to determine the antibacterial effect of each irrigants. After 1 week, patients were recalled for placement of the root canal filling material, zinc oxide and eugenol was applied to the root stumps, and covered with zinc phosphate cement and teeth were finally restored with stainless steel crowns Clinical and radiographic assessments were performed after 3, 6, 9 and 12 months postoperatively. Ninety two patients out of the hundred patients had finished their follow-up.