The necessary and sufficient conditions for multiplicity are derived for isothennal autocatalytic reactions in a nonideal mixing of CSTR with two unpremixed feeds. Cholette’s model is utilized in this paper. The ratio of the fraction of the feed for A to B entering the zone of perfect mixing (n(b)/n(a))(,) is indicated to determine significantly the multiplicity and uniqueness region. When the (n(b)/n(a)) is larger (smaller) than 1, the multiplicity region decreases (increases), and the conversion in active space increases (decreases). When (n(b)/n(a)) is equal to 1, the multiplicity region and the conversion in active space are the same as those in the ideal mixing. If operating in a unique region in the ideal mixing, the system may show multiplicity when (n(b)/n(a)) < 1. On the other hand, if operating in a multiplicity region in the ideal mixing the system may show uniqueness when (n(b)/n(a)) > 1.