Seventeen healthy sub-adult green iguanas (Iguana iguana) naturally infected with oxyurid nematodes were treated to assess the anthelmintic efficacy of a single 25 mg/kg oral dose of oxfendazole. Pooled fecal samples were collected pre-treatment, then weekly for 4 wk post-treatment, and processed the same day via a quantitative double centrifugation technique using Sheather's sugar flotation solution. Total oxyurid egg counts were determined and parasites identified to genus, Ozolaimus or Alaeuris, based on egg morphometry. Fecal egg count reduction (FECR) was then calculated for total oxyurids, total Ozolaimus spp., and total Alaeuris spp. separately for each time point post-treatment. Based on FECR, the single oral dose of oxfendazole was found to be 100% effective (100% FECR) at eliminating nematodes from the GI tract 4 wk post-treatment, without any obvious morbidity or mortality. Additionally, a lack of larvated eggs was observed in the feces as soon as 1 wk post-treatment, with all eggs appearing degenerate at 2 and 3 wk post-treatment. Therefore, the eggs being shed at 3 wk post-treatment were likely nonviable, indicating that oxfendazole was able to impact nematode reproduction prior to reaching 100% efficacy.