In all domains of life, the catalysed degradation of RNA facilitates rapid adaption to changing environmental conditions. We identified a virus-encoded protein that directly binds and inhibits the RNA degradation machinery of its bacterial host, allowing efficient accumulation of viral RNA in the infected cell. Encoded by the giant phage фKZ, KZ37/Dip associates with two RNA binding sites of the RNase E component of the Pseudomonas aeruginosa RNA degradosome. Thereby, KZ37/Dip competes with the binding of RNA substrates, resulting in effective inhibition of RNA degradation. The crystal structure of KZ37/Dip (2.2 Å) reveals an unprecedented fold for which there are no identified structural homologues. The protein forms a homo-dimer that resembles a partially opened scroll and binds RNase E through exposed acidic patches on its convex outer surface. Through the activity of KZ37/Dip, фKZ has evolved a unique mechanism to down regulate a key process of its host.