Simultaneous casting of two polymer solutions allows formation of each membrane layer by different concepts. However, mass transfer between the polymer solutions increases the complexity of the involved phenomena. In the present work, it was investigated the simultaneous casting of two different polymer solutions to form the top and support layers of the membrane, respectively. Polyetherimide and polyethersulfone, were used as base polymers. In order to form the support layer, it was used as a polymer solution composed of Lewis acid:base complex (adipic acid - Lewis acid, and n-methyl-2-pyrrolidone - Lewis base), and another composed of a macromolecular additive (polyvinylpyrrolidone). In order to form the top layer, different polymer solutions composed of a volatile component tetrahydrofuran (THF) were used. The velocity of precipitation of the polymer solutions and the morphology of the membranes were characterized by light transmission measurements and scanning electron microscopy (SEM), respectively. The morphology of the resulting membranes were also compared with the membranes obtained by single casting of each polymer solution. The results mainly showed that adhesion of the membrane layers seemed to occur when there was sufficient time for the solutions to interpenetrate through each other. This was probably favored when the region close to the interface of the solutions remains stable for a longer period. The presence of polyvinylpyrrolidone seemed also to favor adhesion between the layers.