Former Everton Ladies left-sided player Alexander, 22, joined the Women's Super League One club in 2016.
Defender Matthews, 23, who can also play in midfield, has been with the Vixens for six years and helped them reach the 2013 Women's FA Cup final.
Former Aston Villa forward Fergusson, 21, has been with Willie Kirk's side since February.
Newly-promoted Bristol City will play their first 2017 Spring Series game against Reading at Ashton Gate on Saturday, 22 April.
Megan Alexander, Jasmine Matthews and Olivia Fergusson have all signed new deals with Bristol City Women.