The aim of this work is to study by means of dielectric and dynamic-mechanical techniques the miscibility and molecular mobility of sequential interpenetrating polymer networks (IPNs). Sequential poly(butyl acrylate)/poly(butyl methaerylate) interpenetrating networks with different cross-linking densities were prepared using ethylene glycol dimethacrylate as cross-linking agent. Loosely cross-linked IPNs undergo phase separation, as detected by the occurrence of two clearly differentiated main dielectric and dynamic-mechanical relaxation processes corresponding to the two components. Forced compatibilization phenomenon appears in the highly cross-linked IPNs. The IPN cross-linked with 10% EGDMA shows a single main dynamic-mechanical relaxation process. Only the a main relaxation process appears in the PBA networks within the temperature range of the experiments conducted in this work. The dielectric relaxation spectrum of PBMA, networks shows the well-known beta and a relaxation processes, which coalesce in a single alpha beta relaxation in the merging region. In the compatibilized IPNs, both the a and the beta relaxation shift toward lower temperatures as the amount of PBA segments in the IPN increases. The merging region shifts toward lower temperatures as well. In addition to these relaxation processes originated by the homogeneous mixture of PBA and PBMA segments, the IPNs containing more than 50% PBA also show the main PBA's dielectric relaxation process slightly shifted toward higher temperatures. This fact implies that an important part of the PBMA segments is mixed with PBA at the molecular level.