The 2017–18 season of the Belgian First Division B began in August 2017 and ended in April 2018. It was the second season of the First Division B following a change in league format from the old Belgian Second Division. The fixtures were announced near the end of June 2017. Cercle Brugge won the title and promotion on 10 March 2018. Although Tubize lost the relegation play-offs and therefore would have been relegated, they were saved as Lierse went bankrupt.
Source: Belgian First Division B(in French and Dutch) Rules for classification: 1) Points; 2) Matches won; 3) Goal difference; 4) Goals scored; 5) Away goals scored; 6) Away matches won; 7) Play-off.[14]
^The match between Tubize and Beerschot-Wilrijk of 10 December was cancelled as the pitch was not deemed suited for football following long periods of rain and some snow. The match was instead played on 10 January.[15]
In case the team that wins the promotion playoff finishes in the bottom four, the 4th placed team will play the relegation playoff instead.
Promotion play-offs
The winners of the opening tournament and the closing tournament met in a two-legged match to determine the division champion, who promoted to the 2018–19 Belgian First Division A. The team finishing highest in the aggregate table was allowed to play the second leg at home. In case one team had won both the opening and the closing tournament, these matches would not have been played and that team would have been promoted automatically.
On 5 November 2017, Beerschot Wilrijk won the opening tournament and was therefore assured of playing at least the promotion play-offs. The closing tournament was won by Cercle Brugge on 17 February 2018, who played Beerschot Wilrijk for the title and promotion.
The first leg was a closed match with few chances, until Cercle Brugge goalkeeper Paul Nardi made an error in controlling the ball, allowing Euloge Placca Fessou one of the easiest goals of his career. Shortly after, Beerschot Wilrijk saw midfielder Alexander Maes sent off following a harsh tackle, resulting them in controlling the game without creating more chances. In the return match, Cercle Brugge scored twice early and looked on its way to promotion, only for Beerschot Wilrijk to come back to 2–1 just minutes before the end and gaining the advantage on away goals. In a dramatic finish, Cercle Brugge was awarded a last minute penalty kick, converted by Irvin Cardona to bring them back to the highest division where they last played during the 2014–15 season.
The four bottom teams in the aggregate table will take part in the relegation play-offs in which they keep half of the points they collected during the overall regular season (rounded up). As a result, the teams started with the following points before the playoff: Roeselare 18 points, Union SG 16, Westerlo 14 and Tubize 12 points. The points of Roeselare, Westerlo and Tubize were rounded up, therefore in case of any ties on points at the end of the playoffs, their half point would be deducted. The team finishing in last position will relegate to the 2018–19 Belgian First Amateur Division.
Following a 0-1 loss at home to Union SG on 14 April 2018, Tubize was mathematically relegated as the deficit to Union SG became six points with only two matches to go, while Union SG would always be ranked above Tubize in case of ties as the points of Tubize were rounded up prior to the relegation play-offs. Tubize was however spared of relegation from the Belgian First Division B as Lierse did not obtain a Belgian professional football license after going bankrupt.[16]
^As part of the reform, the rules for obtaining a licence were changed, with clubs now required to have a stadium with a capacity of at least 8,000. As the Stade Joseph Marien has only a capacity of six thousand, Union will play one season in the King Baudouin Stadium while their home stadium is being expanded. This ruling was extended with one additional season as the Stade Joseph Marien was not fully refurbished yet at the start of the 2017–18 season and is now expected to be finalised by June 2018.