The crystallinity and thermal degradation behaviours of Polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites have been investigated using differential scanning and thermogravimetry (TGA). The TGA indicates the onset decomposition temperature of D1/2 (half-decomposition) is 16 °C higher for PA6 with 10.0 wt% of OBMFs than that of PA6, whereas the lowest onset decomposition temperature difference among the nanocomposites and neat PA6 is 8 °C for PA6 with 7.5 wt% of OBMFs. However PA6 with 5.0 wt % OBMFs nanocomposite has taken the longest time (1 min 36 s more than neat PA6) to reach D1/2. It can be deduced in this study that PA6 with 5.0 wt % OBMFs nanocomposite provided the maximum heat resistant property whereas PA6 with 7.5 wt % OBMFs nanocomposite showed the maximum heat absorbance property among different nanocomposites and PA6 with 10.0 wt % exhibited the maximum thermal stability. There is a sigmoidal curve generated based on the TIF and wt% filler content value which shows three significant points at intersections of 50% TIF line which are highlighted as exfoliation (4.2 wt%), intercalation (6.8 wt%) and agglomeration (9.0 wt%) points. These TIF values explained the investigated heat resistant, heat capacity and thermal stability properties of PA6/OBMFs nanocomposites illustrating the ratio of TIF and MAF is the key measure which can be considered as an effective approach to identify the nanomorphology of PA6/OBMFs nanocomposites.