An example of a non-Newtonian inkjet ink includes first and second metal oxide nanoparticles, a colorant, an organic solvent, and a balance of water. The first metal oxide nanoparticle has a particle size of 10 nm or less, and is present in an amount ranging from about 5% to about 15% by weight based on a total weight of the ink. The second metal oxide nanoparticle has at least one dimension greater than 10 nm, and is present in an amount ranging from 0.25% to 10% by weight based on the total weight of the ink. The colorant is present in an amount ranging from about 0.5% to about 10% by weight based on the total weight of the ink. The organic solvent is present in an amount ranging from about 5% to about 50% by weight based on the total weight of the ink.