Engineered　cementitious　composites　(ECC)　showed　promising　potentials　in　structural　protection　against　quasistatic　and　dynamic　tension　due　to　their　superior　tensile　ductility.　To　facilitate　its　application　as　reinforcement　layer　of　existing　reinforced　concrete　structures,　the　thickness　effect　of　ECC　in　terms　of　ultimate　tensile　strength　and　tensile　strain　capacity　was　experimentally　investigated.　The　influence　of　the　strain　rate　effect,　the　specimen　thickness,　and　their　coupling　were　examined　and　discussed　in　detail.　It　was　found　that　ECC　exhibited　significant　strain　rate　effect　when　subjected　to　uni-axial　tension　of　strain　rate　ranging　from　10-5　/s　to　100　/s.　Compared　to　those　obtained　from　standard　specimens　under　quasi-static　loading,　the　ultimate　tensile　strength　increased　by　338%,　and　the　tensile　strain　capacity　decreased　by　62%,　respectively,　under　strain　rate　100　/s.　Particularly,　the　strain　rate　effect　was　observed　more　remarkable　under　relatively　higher　strain　rates,　i.e.　from　10　/s　to　100　/s.　Moreover,　subjected　to　a　certain　tensile　loading　rate,　both　the　ultimate　tensile　strength　and　tensile　strain　capacity　decreased　with　increasing　specimen　thickness.　The　degradation　of　strength　was　relatively　slower　under　a　higher　strain　rate,　i.e.　50　/s　and　100　/s,　than　under　a　lower　strain　rate.　To　facilitate　the　design　of　the　ECC　reinforcement　layer,　a　formula　was　proposed　capable　of　predicting　the　ECC　ultimate　tensile　strength　simultaneously　considering　both　the　strain　rate　effect　and　specimen　thickness　effect.