It is a challenge to synthesize transparent polydimethylsiloxane (PDMS) materials that can completely absorb the light energy of ultraviolet (UV) A, B, and C regions. Herein, near‐infrared (NIR) photoluminescent PDMS composites with hydrogen‐terminated silicon nanocrystals (ncSi:H) or decyl‐terminated silicon nanocrystals (ncSi‐decyl) fabricated by combination of hydrosilylation and polymer encapsulation are reported. Their morphologies, optical and mechanical properties, and thermal stabilities are investigated. It is interesting to find that these PDMS composites filled with even a very small amount of ncSi:H or ncSi‐decyl have unprecedented UV‐blocking properties and superior thermal stabilities as compared to the PDMS reference. In particular, the ncSi‐decyl/PDMS composite possesses impressive photoluminescence. Furthermore, ncSi‐decyl are favorable for reinforcing the mechanical properties of the PDMS composites as compared to the PDMS reference and the ncSi:H/PDMS composite. The enhancement in the mechanical properties and thermal stabilities of these novel PL PDMS composites depends upon the creation of crosslinkable sites and entanglement interactions between the PDMS chains and the ncSi. These results suggest that potential applications for NIR photoluminescent ncSi/PDMS composites will likely be found in the fields of advanced UV‐blocking textiles, cosmetics, photofluids, stretchable electronic devices, anticounterfeiting materials, biological imaging, and diagnostics.