Laser　shock　peening　is　an　established　method　used　to　increase　resistance　of　a　surface　to　cracking　and　fatigue　damage　by　inducing　deep　compressive　residual　stresses.　Most　of　the　current　laser　shock　peening　system　utilizes　a　nanosecond　pulse　laser　with　very　slow　repetition　rate　(about　5-10　Hz),　high　pulse　energy　and　a　confining　medium　to　constrain　the　plasma.　On　the　other　hand,　ultrashort　pulse　lasers　generally　have　a　higher　peak　power　density　and　operate　at　higher　repetition　rate　than　nanosecond　pulse　laser.　Therefore,　there　is　an　opportunity　to　employ　ultrashort　pulse　lasers　to　peen　the　surface　in　a　fast　and　efficient　way.　However,　limited　studies　have　been　performed　to　investigate　the　peening　capability　of　ultrashort　laser　pulses.　In　this　study,　femtosecond　(fs)　pulse　laser　is　used　to　peen　a　420　martensitic　steel　surface　under　different　coverage.　The　results　show　that　fs　laser　can　induce　peening　effect;　however,　peened　depths　are　much　smaller　(around　20-30　μm)　compared　to　high　energy　nanosecond　pulse　laser　peening　(up　to　1　mm).　A　maximum　compressive　stresses　of　about　-80　MPa　was　recorded　at　981%　coverage.　Increase　in　coverage　produced　stress　relaxation　and　did　not　increase　the　depth　of　influence.　It　was　found　that　the　state　of　the　residual　stresses　depends　on　four　main　factors　-　intensity　of　ablation-induced　shock　wave,　thermal　effect　of　laser　beam,　phase　transformation　of　the　steel　and　surface　mechanisms　such　as　presence　of　nano-ripples　and　oxidation.　Further　experiments　are　ongoing　to　achieve　higher　magnitude　of　compressive　residual　stresses　and　higher　depth　of　influence.　©　2020　The　Author(s).