NiFe2O4 powders with double skin structure which shows a length of 5 ?m and curved surface thickness of 0.5 ?m were prepared by thermal decomposition of their oxalate precursors. The NiFe2O4 powders were mixed uniformly with a proportion of paraffin and then pressed to composite samples. The electromagnetic parameters of NiFe2O4/paraffin composites with different NiFe2O4 contents were measured by a network analyzer, and the reflection losses were calculated by transmission line theory. The results showed that the 40%(?) NiFe2O4/paraffin composite has the best absorbing property. The minimum reflection loss reaches ?52.06 dB with a sample thickness of 3.5 mm at 6.66 GHz. The effective frequency band of reflection loss less than ?10 dB is 2.73 GHz (6.98?8.59 and 9.72?10.84 GHz) for the sample with a thickness of 3.0 mm.