Sm-Fe-N/Fe　and　Nd-Fe-B/Fe　nanocomposite　magnetic　powders　were　successfully　prepared　by　the　use　of　sonochemistry　to　decompose　the　carbonyl　iron　compounds　in　decane　solvents　containing　Sm-Fe-N　and　Nd-Fe-B　powders　at　low　temperature　and　in　an　inert　atmosphere,　respectively.　The　TEM　observations　and　the　corresponding　EDS　analysis　show　that　the　small　nano-iron　by　sonochemical　process　are　pure　with　a　particle　size　of　about　5　nm.　The　SEM　observations　indicate　that　the　Sm-Fe-N　and　Nd-Fe-B　powders　are　well　coated　by　nano-sized　Fe.　The　content　coating　Fe　can　be　easily　adjusted　by　controlling　the　carbonyl　iron　and　the　related　sonochemical　process.　In　addition,　the　preparation　conditions　and　mechanism　of　coating　process　were　discussed.