In 1721, when Montesquieu published Persian Letters, the word Orientalist was a harmless term for someone who studied or took an interest in Asian and Middle Eastern culture. The term acquired its current pejorative meaning with the publication of Edward Said's Orientalism in 1978. Said argued that these cultures had consistently been portrayed in Western art and literature as exotic, effete, irrational, childish, quarrelsome, and luxurious. These one-dimensional stereotypes of Eastern cultures had then been used as justification for Western imperialism.
Montesquieu's aim in Persian Letters is certainly not explicitly Orientalist. He is not even primarily interested in the culture of Persia, but he merely uses his Persian noblemen, Usbek and Rica, as commentators on the oddities of France. It is Europe, not Persia, that is the target of Montesquieu's satire.
Nonetheless, the book is inadvertently Orientalist in the way it incidentally portrays Persian culture according to traditional stereotypes. This is particularly true at the end of the book, in the letters describing the collapse of the seraglio in Isfahan. Usbek's harem is portrayed as a hotbed of jealousy and intrigue, and an insurrection within it ends in the death of his wives as well as the eunuchs who guard them. This at least suggests that the relative freedom and liberalism of relations between the sexes in France is superior to a system which entails such bloodshed.