Abstract The nylon 6/MgAl layered double hydroxide (MgAl-LDH) nanocomposites have been prepared by melt intercalation of nylon 6 into the part organic dodecyl sulfate (DS) anion-modified MgAl(H-DS) interlayers. The structures and properties of MgAl(H-DS) and corresponding nanocomposites were characterized by ion chromotography, X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), and cone calorimeter test (CCT). The nanoscale dispersion of MgAl(H-DS) layers in the nylon 6 matrix has been verified by the disappearance of d 001 XRD diffraction peak of MgAl(H-DS) and the observation of TEM image. DSC tests evince that these exfoliated MgAl(H-DS) layers play the role of nucleating agents with strong heterogeneous nucleation effect on the crystallization of nylon 6 and increase its crystallization temperature over 12 °C with only 5 wt% MgAl(H-DS). TGA tests show that the effect of alkaline catalysis degradation from LDH on nylon 6 decreases the thermal stability of nylon 6/MgAl-LDH nanocomposites. The data from the cone calorimeter tests show that the HRR and MLR values of the sample with 5 wt% MgAl(H-DS) decrease considerably to 664 kW/m 2 and 0.161 g/m 2 s from 1064 kW/m 2 and 0.252 g/m 2 s of pure nylon 6, respectively. This kind of exfoliated nanocomposite is promising for the application of flame-retardant polymeric materials.