Phosphomimetic substitutions have been instrumental in understanding the role of phosphorylation in protein function. Here we describe the design and construction of a predicted phosphomimetic allele of the JUN kinase kinase gene jkk-1 in C. elegans. To generate the phosphomimetic kinase mutant JKK-1(3E), we edited jkk-1 to introduce three amino acid substitutions, S274E, S278E and S280E. The resulting strain is homozygous viable and extends the survival of L1-arrested larvae. This survival-extending phenotype suggests that the phosphomimetic mutations might promote activation of JKK-1 during the arrest. This jkk-1 potential gain-of-function allele might be useful for studying the regulation and functions of JKK-1.