I just checked in Excel 2008 (what I have at home) and can indeed format a string like "this is a string" in a single cell. Not sure how to do it in Spreadsheet::WriteExcel, but it might be possible to save the same file with just a single filled cell in it, where the bold part is the only difference and figure it out

http://search.cpan.org/tools/Spreadsheet-WriteExcel-2.40 -> http://search.cpan.org/grep?cpanid=JMCNAMARA&release=Spreadsheet-WriteExcel-2.40&string=bold&i=1&n=1&C=0#examples/colors.pl

2499:You can specify the font of a section of the text by prefixing it
+ with the control sequence C<&"font,style"> where C<fontname> is a fo
+nt name such as "Courier New" or "Times New Roman" and C<style> is on
+e of the standard Windows font descriptions: "Regular", "Italic", "Bo
+ld" or "Bold Italic":
2502:    $worksheet2->set_header('&C&"Courier New,Bold Italic"Hello');
2760:               Bold              bold            set_bold()
[download]

So the docs say its a set_header feature ... I'd try it with cells to see if it works

Thanks but it doesn't seems to work - it print the string as is (&C&"Courier New,Bold Italic"Hello).

Thanks but it just print the string ('&C&"Courier New,Bold Italic"Hello') when using $worksheet2->write(1,2,'&C&"Courier New,Bold Italic"Hello')...