The invention relates to a process for preparing β-aminopropionic acid derivatives by reacting a primary or secondary amine with an acrylic acid derivative, wherein comprises (i) a first primary or secondary amine is provided as an amine of value and reacted with the acrylic acid derivative, to obtain a reaction mixture comprising a first β-aminopropionic acid derivative as a product of value and additionally unconverted acrylic acid derivative, (ii) the unconverted acrylic acid derivative present in the reaction mixture is reacted with a second secondary amine as a scavenger amine virtually fully to give a second β-aminopropionic acid derivative to obtain a reaction mixture comprising the first β-aminopropionic acid derivative as a product of value, the second β-aminopropionic acid derivative and unconverted secondary amine.