Rapid development of electronic devices and advanced technology creates more electromagnetic wave interference that is harmful to human health as well as equipment. Thus, the use of electromagnetic (EM) wave absorber becomes more focused among researchers and attracted more public attention. Carbon nanocoils (CNs) have been introduced due to its chemical, physical and mechanical properties that can produce lightweight, wide absorption range and strong absorption. This research highlights the use of mixed ferrites (Fe3O4 and CoFe2O4) as catalyst to grow carbon nanocoils. Different weight percentages of Fe3O4 and CoFe2O4 were mixed to grow carbon nanocoils and further used as fillers to be incorporated into epoxy matrix. The morphological study of synthesized carbon nanocoils and reflection loss of the prepared polymer composites were studied in the range of X-band and Ku-band at thickness 1 mm, 2 mm, and 3 mm. The reflection loss achieved shows that mixed ferrites as catalyst to grow carbon nanocoils have great potential to be used as an excellent EM wave absorbers at low thickness.