Significance Biological processes take place in living cells and have adapted to environmental conditions such as temperature, salt concentration, and high-density cellular contents. However, our molecular understanding of most biological processes relies on in vitro experiments under nonphysiological, highly diluted, and high-salt conditions. To overcome this, we mimic the cellular environment by introducing crowding agents. To understand how such conditions affect large-ribozyme folding and function, we studied a group IIB intron ribozyme under crowded, low-salt conditions. The data show how crowded environments enhance the activity of such large ribozymes, even in low-salt concentrations. Interestingly, we find that “optimal” crowding yields maximum activity, beyond which dense crowding becomes detrimental for activity.