Complexes of cell-THPC-thiourea-ADP with transition metal ion Ni2+, Fe2+, and Cu2+ and lanthanide metal ions Gd3+, Dy3+, and Tb3+ have been prepared. The thermal stability and smoke suspension of the samples are determined by thermogravimetry (TG), differential thermal analysis (DTA), and cone calorimetry. The activation energies for the second stage of thermal degradation have been obtained by following the Broido equation. Experimental data show that for the complexes of cell-THPC-thiourea-ADP with the metal ions, the activation energies and thermal decomposition temperatures are higher than those of cell-THPC-thiourea-ADP, which shows these metal ions can increase the thermal stability of cell-THPC-thiourea-ADP. Moreover, these lanthanide metal ions can more increase thermal stability of samples than do the transition metal ions. The cone calorimetry data indicate that the lanthanide metal ions, similar to transition metal ions, greatly decrease the smoke, CO, and CO2 generation of cell-THPC-thiourea-ADP, which can be used as smoke suppressants. However, there are no obvious effects for these metal ions on heat release of samples.