Gustav Kastropp (30 August 1844 – 11 September 1925) was a German poet, librettist and musician.
Kastropp's texts were used by composers such as Georg Schumann, Eugen d'Albert and Bernhard Stavenhagen.
He went to Gymnasium in Göttingen and just like his father he worked as a pharmacist.
He studied music at the conservatories in Stuttgart, Göttingen and Sondershausen.
From 1874 to 1877 he taught literature at the Großherzogliche Orchesterschule in Weimar.