Carbon nanotube and Fe3O4 based magnetic composites have been prepared by dispersing acid treated CNTs in the precursor solution required for the synthesis of Fe3O4. The different weight percentage of CNTs has been mixed in ionic solution of Fe3O4. The various properties like crystalline nature, morphology and free electron spin concentration have been investigated to characterize the composites. The XRD pattern and SEM images of composites confirmed that the composites have been synthesized successfully by chemical co-precipitation technique. The free electron spin concentrations have increased with the increasing weight percentage of CNTs. The varying free electron concentration confirmed the varying weight percent of CNTs and enhanced magnetic nature of composites.