A new wurtzite phase of copper tin selenide (CTSe) was discovered, and the resulting nanocrystals were synthesized via a facile solution-phase method. The wurtzite CTSe nanocrystals were synthesized with dodecylamine and 1-dodecanethiol as coordinating solvents and di-tert-butyl diselenide ((Bu2Se2)-Bu-t) as the selenium source. Specific reaction control (i.e., a combination of 1-dodecanethiol with (Bu2Se2)-Bu-t) was proven to be critical in order to obtain this new phase of CTSe, which was verified by powder X-ray diffraction and selected area electron diffraction. The wurtzite CTSe nanocrystals possess an optical and electrochemical band gap of 1.7 eV and display an electrochemical photoresponse indicative of a p-type semiconductor.