diff --git a/example_test.go b/example_test.go
index 2117bb6..9ece6b5 100644
--- a/example_test.go
+++ b/example_test.go
@@ -10,6 +10,15 @@ func ExampleOpen() {
 	}
 }
 
+func ExampleNumberSheets() {
+	if xlFile, err := Open("Table.xls", "utf-8"); err == nil {
+		for i := 0; i < xlFile.NumSheets(); i++ {
+			sheet := xlFile.GetSheet(i)
+			fmt.Println(sheet.Name)
+		}
+	}
+}
+
 //Output: read the content of first two cols in each row
 func ExampleWorkBook_GetSheet() {
 	if xlFile, err := Open("Table.xls", "utf-8"); err == nil {
diff --git a/workbook.go b/workbook.go
index a6a4830..d80984d 100644
--- a/workbook.go
+++ b/workbook.go
@@ -210,16 +210,24 @@ func (w *WorkBook) prepareSheet(sheet *WorkSheet) {
 	sheet.parse(w.rs)
 }
 
+//Get one sheet by its number
 func (w *WorkBook) GetSheet(num int) *WorkSheet {
 	if num < len(w.sheets) {
 		s := w.sheets[num]
-		w.prepareSheet(s)
+		if !s.parsed {
+			w.prepareSheet(s)
+		}
 		return s
 	} else {
 		return nil
 	}
 }
 
+//Get the number of all sheets, look into example
+func (w *WorkBook) NumSheets() int {
+	return len(w.sheets)
+}
+
 //helper function to read all cells from file
 func (w *WorkBook) ReadAllCells(max int) (res [][]string) {
 	res = make([][]string, 0)
diff --git a/worksheet.go b/worksheet.go
index 50b2cf4..bad4cf9 100644
--- a/worksheet.go
+++ b/worksheet.go
@@ -22,6 +22,7 @@ type WorkSheet struct {
 	Rows map[uint16]*Row
 	//NOTICE: this is the max row number of the sheet, so it should be count -1
 	MaxRow uint16
+	parsed bool
 }
 
 func (w *WorkSheet) parse(buf io.ReadSeeker) {
@@ -39,6 +40,7 @@ func (w *WorkSheet) parse(buf io.ReadSeeker) {
 			break
 		}
 	}
+	w.parsed = true
 }
 
 func (w *WorkSheet) parseBof(buf io.ReadSeeker, b *bof, pre *bof) *bof {