The 2005–06 National Division One was the 19th full season of rugby union within the second tier of the English league system, currently known as the RFU Championship.

New teams to the division included Harlequins who had been relegated from the 2004–05 Zurich Premiership, while Doncaster and Newbury were promoted from the 2004–05 National Division Two.

[1][2][3] Additional changes saw Penzance & Newyln RFC rebrand themselves as the Cornish Pirates as well as moving from their home ground, the Mennaye Field in Penzance, to a more central location in Truro at the Kenwyn Rugby Ground (a temporary stadium built in the city) with the aim to appeal more to Cornish fans on the whole as well as making home games more accessible.

[6] Bedford Blues finished in second place and there was no relegation to National Division Two following the RFU's decision to expand National Division One from 14 to 16 teams for the 2006–07 season.

[7][8] [10] [11] [12] 70 - 5 Harlequins at home to Exeter Chiefs on 22 October 2005 68 - 16 Bedford Blues away to Pertemps Bees on 11 March 2006 79 - 22 Bedford Blues at home to Newbury on 29 April 2006 Harlequins at home to Exeter Chiefs on 22 October 2005 Bedford Blues at home to Newbury on 29 April 2006 Bedford Blues at home to Newbury on 29 April 2006 Coventry at home to Newbury on 11 March 2006 Plymouth Albion at home to Exeter Chiefs on 3 September 2005 [13][14][15][16] Alastair Hepher for Bedford Blues at home to Newbury on 29 April 2006 Richard Welding for Cornish Pirates at home to Earth Titans on 18 September 2005 Ugo Monye for Harlequins at home to Exeter Chiefs on 22 October 2005 Alastair Hepher for Bedford Blues at home to Newbury on 29 April 2006 James Moore for Coventry at home to Newbury on 11 March 2006 N/A - multiple players [17][18][19][20][21] Harlequins at home to Plymouth Albion on 29 April 2006 Sedgley Park at home to Newbury on 18 February 2006 Harlequins Orrell [22]