The shot stopper was named Man of the Match on three occasions for the Eagles' six matches in December, keeping two clean sheets in the process and conceding just four goals.
The Spaniard pulled off a collection of impressive saves across the month and received the fans' recognition with 51% of the votes cast, beating Jordan Ayew on 27% to the award.
Having picked up his trophy, Guaita said: "For me, it's important this month. Another Player of the Month - I'm happy but the important thing is my team. For me, it's the best because another goalkeeper, my mates, a lot of days their work is hard for me.
"I'm playing and my performances are good because of my mates. I'm happy for me, for my family and all the people near me. It's good. For the fans, I need more saves because I want Crystal Palace in the Premier League next year."