This paper investigated the effect of carbon nanotubes (CNTs) on the electromagnetic interference shielding of carbon fiber reinforced polymer (CFRP) composites. The CNT/CFRP composites were fabricated by dry spray deposition of CNT on surfaces of carbon fiber prepregs and then out‐of‐autoclave curing process. The interlaminate shear strength of CNT/CFRP composites was first examined. It was found that the shear strength was strengthened if the CNT loading between prepregs was below 3.0 g/m2. Then, the electromagnetic interference shielding effectiveness (EMI SE) of CNT/CFRP composites was characterized as a function of CNT loadings over the X‐band frequency range (8.2–12.4 GHz). The tests revealed that the maximum and minimum EMI SE of CNT/CFRP composites increased by approximately 20%, from 62 to 74 dB and from 45 to 53 dB, respectively, by adding 2.5 g/m2 CNT at the interlaminate surfaces. The results unveiled that the shielding by absorption dominates in the overall EMI SE of CNT/CFRP composites, while the shielding by reflection is almost independent of CNT loadings. It was also observed that the overall EMI SE increased linearly with CNT loading. This study shows that the spray deposition of CNT is an efficient technique to improve the EMI shielding performance of CFRP composites. POLYM. COMPOS., 39:E655–E663, 2018. © 2016 Society of Plastics Engineers