Boolean network (BN) is a popular mathematical model for studyinggenetic regulatory networks and its observability plays avital role in understanding the underlying network.Several research works have been done onobservability of BNs and complex networks.However, observability of attractor cycles is not yet fully addressedin the literature and it is a challenging issue.In this paper, we propose a novel problem on theobservability of attractors in a BN.Identification of the minimum set of contiguous nodes that can determinewhich attractor cycle the system belongs tocan serve as a biomarker for different disease types (different attractors).Thus, detection of the minimum set plays a significant role inthe study of signaling networks.We propose a novel method for solvingthe problem in O(n) time where n is the number of genes in the network.Furthermore, computational experiments are conductedto demonstrate both the efficiency and the effectiveness ofour proposed method for the captured observability problem.