A　remote　sensing　based　ecological　index　(RSEI)　was　developed　specially　for　monitoring　and　assessing　regional　ecological　changes.　The　index　combined　four　indicators　from　existing　remote-sensing　indices/components　to　represent　greenness,　dryness,　wetness　and　heat,　which　were　the　important　ecological　indicators　frequently　used　in　assessing　regional　ecology.　Instead　of　a　weighted　addition　of　the　four　indicators,　the　principal　component　analysis　(PCA)　was　utilized　to　compress　the　four　indicators　into　one　in　order　to　assess　overall　regional　ecological　status.　The　RSEI　was　then　constructed　using　the　first　component　(PC1).　The　application　of　RSEI　in　Hetian　area　of　County　Changting　in　Fujian　Province,　China,　showed　that　the　RSEI　could　quantitatively　reveal　regional　ecological　changes　during　the　period　from　1988　to　2010.　The　RSEI　values　could　be　well　compared　with　the　commonly-used　ecological　index　(EI).　Nevertheless,　besides　working　as　a　quantitative　indicator,　the　RSEI　had　more　functions　than　the　EI,　such　as　detecting,　simulating　and　predicting　spatiotemporal　changes　of　regional　ecological　quality.