The objective of this study is to determine the effects of dolomite content on flammability, thermal and mechanical properties of polybutylene terephthalate (PBT)/ dolomite composites. PBT and dolomite were blended together at different dolomite contents (5 wt%, 10 wt% and 15 wt%) via twin screw extruder prior to injection moulding. Limiting oxygen index (LOI) test was used to determine the flammability of the PBT composites. Degree of crystallisation (Xc), glass transition (Tg), melting (Tm) and crystallisation (Tc) temperatures were obtained using differential scanning calorimetry (DSC). Three types of mechanical tests were carried out, i.e., flexural, tensile and Izod impact. Morphological study was characterised using scanning electron microscope (SEM). LOI analysis showed that the incorporation of dolomite reduced the flammability of PBT composites. DSC results showed that dolomite has marginal effect on Tg and Tm of the PBT composites. On the other hand, Tc and Xc increased with increasing dolomite content which indicates that it can be used as a nucleating agent. The presence of dolomite increased the flexural properties, tensile strength and Young’s modulus of PBT composites. However, the elongation at break and impact strength were significantly decreased due to poor adhesion between dolomite and PBT. PBT/D-15 composite was found to have the optimum mechanical properties compared with other PBT/dolomite composites. SEM micrograph revealed that dolomite is uniformly distributed at lower dolomite content but agglomerated at higher content.