Poly{bis[(trimethylsilylethynyl)phenyl]silylenephenylene}s (2a - d) were prepared by the re actions of the respective poly[(diethoxysilylene)phenylene]s with (trimethylsilylethynyl)phenyllithium. Desilylation of the resulting polymers 2a-d with K2CO3/MeOH gave poly{[bis(ethynylphenyl)silylene]phenylene}s (3a-d). Polymers 3a-d exhibit extremely high heat-resistance and their thermogravimetric analysis (TGA) in a nitrogen atmosphere shows the temperature of 5% weight loss (T-d5) of 651-711 degrees C. Total weight loss at 1000 degrees C in TGA was determined to be 8-10% based on the initial weight. Thermal differential analysis (TDA) of the polymers reveals an exothermic peak around 220 degrees C probably due to cross-linking reactions concerning ethynyl groups. TGA of the polymers shows a high T-d5 of 436-566 degrees C even in air, although the total weight loss at 1000 degrees C was 76-81% of the initial weight, much higher than that in nitrogen.