A laminar flow process for preparing cellulose diacetate fibers is disclosed. In the process, a precipitation-acid stream and an acid-dope stream are contacted in a zone having substantially laminar flow. The acid-dope stream is annularly disposed within and flows in the same direction as the precipitation-acid stream. The precipitation-acid stream has a temperature of 100.degree. to 200.degree. F. and comprises 25 to 35 percent by weight acetic acid and 75 to 65 percent by weight water. The acid-dope stream has a temperature in the range of 100.degree. to 200.degree. F. and comprised of 5 to 22 weight percent of cellulose diacetate having an inherent viscosity of at least 1.0, and 95 to 78 percent by weight of a mixture comprising 65 to 90 weight percent acetic acid and 35 to 10 weight percent water. The precipitation-acid stream has a linear flow greater than or equal to the linear flow of the acid-dope stream. The weight ratio of the precipitation-acid stream to the acid-dope stream is at least 9:1. Contacting the two streams in this manner causes precipitation of cellulose diacetate fibers of predictable diameter as the two streams diffuse together.