This paper investigates empirically the influence of regulation logic on the dynamics of two computational models of genetic regulatory network motifs. The gene regulatory network motifs considered in this work consist of three genes with both positive and negative feedback loops. Two forms of fuzzy logic, namely, the Zadeh operators and the probabilistic operators, as well as the summation logic have been investigated. We show that the easiness of evolving sustained oscillation, and the stability of the evolved oscillation depend both on the regulation logic and on the consistency of the regulation on the target gene.