Can I use my middle name as my last name for publishing my book?

You can use whatever name you like on your book. Lots of the most famous authors in the world have used different names to publish their work, and some of them even use names of the opposite sex. The Victorian novelist George Eliot was actually a woman called Maryanne Evans. George Orwell's real name was Eric Blair. Charlotte, Emily and Anne Bronte originally had their books published under the names Currer, Ellis and Acton Bell. Ruth Rendell publishes some books as Ruth Rendell and some as Barbara Vine. There are countless other examples. Some writers choose different names altogether. Some use their middle names, or their mother's maiden name, or whatever.

If you consider your friends asking why your name is different on your book cover to be a 'problem', then you must have had a charmed life. It's hardly a 'problem' to tell your friends that you used your middle name as a pen-name, is it? Not exactly arduous. Honestly, if that's an example of something that's a 'problem' to you, then I worry that you aren't cut out for the publishing business, because it's full of hard work and rejection.

May I ask if you're self-publishing your book - ie, are you paying a company yourself to publish it? Because if you are, that's not 'real' publishing. I ask because if you had a proper publisher - ie, a publisher who pays YOU for the privilege of publishing your book, not the other way around - they would be advising you on things like pen-names and you wouldn't need to ask people on Yahoo Answers.

I don't see why not. There are a bunch of authors out there who use (or have used) pen names.

um...are you sure you'd get published? I don't really want to burst your bubble or anything, but getting published is really hard.