The Sadducees were a group of priests who had a lot of influence and control in Jerusalem. Generally they were quite wealthy and politically connected, often being members of the local aristocracy1 with a seat on the Sanhedrin. They only accepted the authority of the Torah (Genesis, Exodus, Leviticus, Numbers, and Deuteronomy) and did not believe in the resurrection from the dead. In contrast with the Gospel of Luke where the Pharisees are seen as the major opponents of Jesus, in Acts, it is the Sadducees who seem to take over this role. Most likely this is because a lot of action takes place in Jerusalem, which was also the area where they were most prominent.2
17 But the high priest rose up, and all who were with him (that is, the party of the Sadducees), and filled with jealousy