Objective: To investigate and compare the impact of pre-heating of an ormocer-based and a methacrylate-based restorative materials at different temperature on intra-pulpal temperature with that at room temperature. Materials and Methods: In the current study, two bulk-fill composite systems; one ormocer-based, and one methacrylate-based were used according to their manufacturer instructions.  A total of 30 sound maxillary human molars was selected, and prepared by removal of occlusal enamel and part of dentin till remaining dentin thickness becomes 2 mm above highest pulp horn. The specimens were assigned equally into two halves, according to type restorative material used (n=15 for each). For every restorative system; each group was further subdivided into three subgroups according to the pre-heating regimen (non pre-heated, 540 C or 600 C). A K-type thermocouple was placed inside tooth pulp chamber. The intra-pulpal temperature was measured in each specimen before, after composite placement and after curing of restorative material, also after 15sec, 30sec, 60sec. Results: The outcome of three-way ANOVA revealed that the type of composite material, different heating temperature and different restorative stages had a statistical significant effects on intra-pulpal temperature values (p < 0.05). Post-hoc Tukey test outcome showed that, the ormocer-based composites showed significant intra-pulpal temperature increase compared to methacrylate-based composites. Conclusions: On the basis of the results of the current study, it seems reasonable to conclude that there is a proof that heating of composite restorative materials increase the intra-pulpal temperature with a noticeable increase in pre-heating of ormocer compared to methacrylate-based composite.