In　this　article,　a　novel　spacetime　collocation　Trefftz　method　for　solving　the　inverse　heat　conduction　problem　is　presented.　This　pioneering　work　is　based　on　the　spacetime　collocation　Trefftz　method;　the　method　operates　by　collocating　the　boundary　points　in　the　spacetime　coordinate　system.　In　the　spacetime　domain,　the　initial　and　boundary　conditions　are　both　regarded　as　boundary　conditions　on　the　spacetime　domain　boundary.　We　may　therefore　rewrite　an　initial　value　problem　(such　as　a　heat　conduction　problem)　as　a　boundary　value　problem.　Hence,　the　spacetime　collocation　Trefftz　method　is　adopted　to　solve　the　inverse　heat　conduction　problem　by　approximating　numerical　solutions　using　Trefftz　base　functions　satisfying　the　governing　equation.　The　validity　of　the　proposed　method　is　established　for　a　number　of　test　problems.　We　compared　the　accuracy　of　the　proposed　method　with　that　of　the　Trefftz　method　based　on　exponential　basis　functions.　Results　demonstrate　that　the　proposed　method　obtains　highly　accurate　numerical　solutions　and　that　the　boundary　data　on　the　inaccessible　boundary　can　be　recovered　even　if　the　accessible　data　are　specified　at　only　one-fourth　of　the　overall　spacetime　boundary.