The calcium-regulated heat-stable protein of 24 kDa (CRHSP-24) is a major calcineurin phosphoprotein that functions in multiple signal transduction pathways in cell metabolism. Schistosomes are multicellular parasites that infect 200 million people worldwide, even though treatment has been available for two decades. To determine the function of schistosome CRHSP-24 (SjCRHSP-24), we successfully knocked down SjCRHSP-24 in Schistosoma japonicum by RNA interference (RNAi). By establishing controls for measuring off-target RNAi effects, we found that different double-stranded (dsRNA) sequences had different levels of effectiveness. While all tested dsRNAs reduced CRHSP-24 transcript levels, the S2 dsRNA consistently reduced CRHSP-24 expression to >95% of the control. Knockdown of the SjCRHSP-24 gene significantly affected the morphology and vitality of S. japonicum.