Zinc oxide nanoparticles were produced by aqueous precipitation in mild hydrothermal conditions (90 ◦C). Well crystallized regular roundish particles were obtained, with a very narrow size distribution. The influence of soft templates (organic species) to control size and size distribution in the final product was investigated. No effect was observed with polyvinylpyrrolidone (PVP Mw 8000 and 40,000), (d−)fructose and hydroxypropylmethylcellulose (HPMC). A significant decrease of the particle size towards 100 nm, while conserving a very narrow size distribution was observed for poly(acrylic acid) (PAA Mw 2000), Dispex A40 (commercial PAA from CIBA Mw ∼10,000), and sodium dodecylsulfate (SDS). The influence of the pHwas also investigated with PAA. By increasing the pH from slightly acidic to basic conditions, the morphologywas spectacularly modified from roundish nanoparticles to micronic branched flower-like particles, with an elongated primary crystal morphology.