Stretchable　synaptic　transistors　(SSTs)　are　of　paramount　importance　for　the　development　of　soft　machines　and　neuromorphic　systems.　Unfortunately,　the　reports　about　SSTs　are　very　limited　and　more　importantly,　the　impact　of　the　mechanical　deformations　that　occur　in　stretchable　electronics　during　practical　applications,　on　the　behavior　of　SSTs　has　never　been　reported.　In　this　work,　a　simple　and　universal　method　was　introduced　to　fabricate　a　stretchable　organic　synaptic　transistor　using　wavy　networks　P3HT　nanofibers　as　a　semiconductor　and　the　effect　of　mechanical　deformation　on　its　behavior　at　different　deformation　states　is　investigated　for　the　first　time.　Our　SSTs　exhibited　excellent　mechanical　stability　even　after　experiencing　large　stretching　deformation.　More　importantly,　our　results　demonstrated　that　the　learning　and　memory　behavior,　and　the　decay　constants　of　synaptic　transistors,　which　are　among　the　most　important　parameters　for　biologic　sensory　neurons,　can　be　tuned　by　mechanical　deformation,　which　is　associated　with　mechanical　deformation　dependant　ion　transport　in　ion-gel.　These　results　offer　a　promising　direction　for　utilizing　mechanical　deformation　to　develop　different　functional　devices.　Our　SSTs　with　tunable　synaptic　behavior　can　facilitate　the　development　of　wearable　and　implantable　artificial　neuromorphic　systems　and　soft　machines.　©　2020　Elsevier　Ltd