This study investigates whether university students' epistemic beliefs and prior knowledge about controversial socioscientific issues (SSIs) can predict the different types of arguments that students construct. Two hundred forty-three university students were asked to construct different types of supportive arguments--social, ethical, economic, scientific, ecological--as well as counterarguments and rebuttals after they had read a scenario on a SSI. Participants' epistemic beliefs and prior knowledge were assessed separately. Results showed that students' epistemic beliefs and prior knowledge predicted the quantity, quality, and diversity of the different types of arguments the students constructed. In particular, students who held sophisticated epistemic beliefs about the structure of knowledge and exhibited relatively "more robust" prior knowledge scores, produced arguments of greater quantity, better quality, and higher diversity than students with less sophisticated epistemic beliefs and low prior knowledge scores. Educational implications are discussed.