Ribonucleic acids (RNAs) can self-assemble and catalyze chemical reactions. It has been proposed that such RNA molecules could have played crucial roles in the origins of life. However, the spontaneous formation of these RNA molecules, with their complex structures and enzymatic functions, remains a major challenge. Here, we show that RNA ribozymes, small catalytic RNA molecules, can assist each other in their self-assembly and enzymatic reactions. Through in vitro selection experiments, we identified a pair of cooperative ribozymes that can spontaneously form a mutually stabilizing complex and catalyze two sequential chemical reactions. Our results provide experimental support for the notion that RNA molecules could have facilitated their own emergence through cooperative interactions and demonstrate a potential mechanism for the functional diversification of RNA molecules in prebiotic environments.