The　smart　contract　is　an　interdisciplinary　concept　that　concerns　business,　finance,　contract　law　and　information　technology.　Designing　and　developing　a　smart　contract　may　require　the　close　cooperation　of　many　experts　coming　from　different　fields.　How　to　support　such　collaborative　development　is　a　challenging　problem　in　blockchain-oriented　software　engineering.　This　paper　proposes　SPESC,　a　specification　language　for　smart　contracts,　which　can　define　the　specification　of　a　smart　contract　for　the　purpose　of　collaborative　design.　SPESC　can　specify　a　smart　contract　in　a　similar　form　to　real-world　contracts　using　a　natural-language-like　grammar,　in　which　the　obligations　and　rights　of　parties　and　the　transaction　rules　of　cryptocurrencies　are　clearly　defined.　The　preliminary　study　results　demonstrated　that　SPESC　can　be　easily　learned　and　understood　by　both　IT　and　non-IT　users　and　thus　has　greater　potential　to　facilitate　collaborative　smart　contract　development.　©　2018　IEEE.