Two-dimensional　(2D)　transition　metal　dichalcogenides　(TMDs)　room　temperature　(RT)　gas　sensors　are　of　great　value　for　monitoring　leaks　of　hazardous　gases　under　harsh　environments.　However,　the　highly　sensitive　and　rapid　detection　of　TMDs　in　an　energy-efficient　state　is　still　a　formidable　obstacle.　This　work　reports　the　ultrasensitive　NO2　sensor　based　on　rare-earth　Nd　doped　VS2/carbon　nanofibers　(CNFs)　(abbreviated　as　x%Nd-VS2-C),　which　exhibits　a　fast　response/recovery　and　intense　response　at　RT.　The　impact　of　the　Nd　doping　amount　on　the　NO2-sensing　properties　of　x%Nd-VS2-C　was　systematically　explored.　The　active　Nd-doping　and　abundant　S　vacancies　could　activate　the　inert　basal　planes　of　VS2　efficiently　and　increase　the　active　sites　of　the　surface,　thereby　improving　the　NO2-sensing　performance　of　the　sensor.　Additionally,　theoretical　calculations　validate　the　finding　by　demonstrating　a　more　negative　NO2　adsorption　energy　of　-3.12　eV　on　the　(001)　surface　of　Nd-VS2-C　compared　to　-1.26　eV　on　pure　VS2.　The　2%　Nd-VS2-C　exhibits　optimal　RT　NO2-sensing　properties,　with　a　thrilling　response/recovery　rate　(similar　to　17　s/20　s),　high　sensitivity　(similar　to　3.03　to　10　ppm　of　NO2),　favorable　selectivity　and　stability,　and　low　detection　limit　(18　ppb).　The　outstanding　＂＇4S＇＂　features　make　the　2%Nd-VS2-C　sensor　greatly　attractive　for　precise　and　ultrasensitive　NO2　detection　at　RT.