Small interfering RNAs (siRNAs) and microRNAs (miRNAs) mediate gene silencing through evolutionarily conserved pathways. In Caenorhabditis elegans, the siRNA/miRNA pathways are also known to affect transgene expression. To identify genes that regulate the efficiencies of the siRNA/miRNA pathways, we used the expression level of a transgene as an indicator of gene silencing and isolated a transgene-silencing mutant, adbp-1 (ADR-2 binding protein). The adbp-1 mutation caused transgene silencing in hypodermal and intestinal cells in a cell-autonomous manner, depending on the RNA interference (RNAi) machinery. The adbp-1 gene encodes a protein with no conserved domains that is localized in the nucleus. Yeast two-hybrid screening and co-immunoprecipitation analysis demonstrated that ADBP-1 physically interacts with ADR-2, an RNA-editing enzyme from the ADAR (adenosine deaminase acting on dsRNA) family. In the adbp-1 mutant, as previously shown in adr-2 mutants, A-to-I RNA editing was not detected, suggesting that ADBP-1 is required for the RNA-editing activity of ADR-2. We found that ADBP-1 facilitates the nuclear localization of ADR-2. ADBP-1 may regulate ADR-2 activity and the consequent RNA editing and thereby antagonize RNAi-mediated transgene silencing in C. elegans.