Is it worth visiting Sevilla's Royal Alcazar if we visit Alhambra in Granada? If so, how long will it take us to visit it?

Yes! The visit should take an hour or so.

Yes, a totally different thing, despite the architectural similarities. Most of it was constructed in Arab style by Christian rulers in the 14th Century (Sevilla fell to the Christians in 1248), and the Real Alcázar thus stands as one of the best example of mudejar architecture in all of Spain. Visited just a month ago. Stunningly beautiful. You could easily spend several hours here, and you could completely loose yourself in the gardens. It's now the residence of the king and queen when in Sevilla.

In some ways we enjoyed the Alcazar even more than the Alhambra but I think they are both worth a visit. And I would also agree that there are a LOT of "architectural similarities" as well as interior decoration similarities.

Oh yes

I visited both as well, but loved Al Hambra more.. a must see , since you are there!

I agree that they are both worthy of a visit. As I recall, I spent about an hour in the Alcazar itself and about an hour in the gardens; I could easily have spent much longer in the gardens. Enjoy!

I would say that it's definitely worth it, but that you should see the Alcazar before seeing the Alhambra if you can manage it. I visited both this past spring, seeing first Sevilla and then Grenada. The Alcazar is a beautiful palace that I'm glad I saw--especially the gardens. The Alhambra though is something special, and was my favorite part of the trip. It might have been anticlimactic for me to see them in the opposite order.