The 26-year-old, who departed Venda Nova for Zagreb in 2006, scored 12 times in 23 matches last season.
"Since I was a child, I wanted to play in Spain," Sammir told reporters at his official unveiling.
"I was at Dinamo Zagreb a long time, seven years, and need other challenges. I like the technical Spanish style and hope I'll be happy here and that the club and fans are happy with me."
Sammir has four international caps to his name.