Titanium dioxide is a compound that is used in the food, cosmetic, and paint industries; however, it is still toxic to humans and the environment. This study determined the toxicities of titanium dioxide nanoparticles (TiO₂ NPs) in a Caenorhabditis elegans (C. elegans) model. The effects of commercially available (C-TiO₂) and synthetically (S-TiO₂) prepared TiO₂ NP solutions on lethality, lifespan, growth, reproduction, locomotion, and gene expression were studied in C. elegans. Exposure to TiO₂ NPs (0.0, 0.01, 0.1, 1.0, and 10 mg/L) did not result in any change to the survival rate or body length of the nematodes, regardless of the concentration. However, there was a decrease in the reproduction (brood size) and locomotion (body bending and head thrashing) of the nematodes as the TiO₂ NP concentration increased. The longevity of the nematodes was shortened following TiO₂ NP exposure. The gene expression of sod-1, sod-3, ctl-1, ctl-2, cyp35A2, mlt-1, and mlt-2 in the nematodes showed that there was an overexpression of all genes when the worms were exposed to 1 mg/L C-TiO₂ or 10 mg/L S-TiO₂. It was therefore concluded that compared with S-TiO₂, C-TiO₂ possibly causes more toxicity or genotoxicity in the C. elegans model.