Provided is a separation membrane support comprising a nonwoven fabric and having excellent membrane formability that achieves a high and stable yield when the separation membrane support supports various separation membranes such as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes, having excellent processability when a fluid separation element is produced, and having excellent mechanical strength. Also provided are a separation membrane and a fluid separation element using the separation membrane support and having high membrane peel strength. The separation membrane support comprises a nonwoven fabric. The nonwoven fabric has a boiling water shrinkage of -0.2 to 2.0% in the length direction (longitudinal direction) after treatment in boiling water for 5 minutes. The separation membrane is prepared by forming a membrane having a separation function on a surface of the separation membrane support. The fluid separation element comprises the separation membrane as a constituent.