This paper evaluates the potential of oxidized single-walled carbon nanohorns (o-SWNHs) immobilized on the pores of a hollow fiber (HF) for the direct immersion solid-phase microextraction of triazines from waters. The fabrication of the device requires the oxidation of the nanoparticles by means of microwave irradiation in order to obtain a homogeneous dispersion in methanol. Then, a porous hollow fiber is immersed in the methanolic dispersion of the o-SWNHs under ultrasound stirring. This procedure permits the immobilization of the o-SWNHs in the pores of the hollow fiber. For the extraction, a stainless steel wire was introduced inside the fiber to allow the vertical immersion of the o-SWNHs-HF in the aqueous standard/water sample. The triazines were preconcentrated on the immobilized o-SWNHs and further eluted using 150 μL of methanol. The solvent was evaporated and the residue reconstituted in 10 μL of methanol for sensitivity enhancement. Gas chromatography-mass spectrometry was selected as instrumental technique. The limits of detection were between 0.05 and 0.1 μg L(-1) with an excellent precision (expressed as relative standard deviation) between runs (below 10.2 %) and between fibers (below 12.8 %). Finally, the method was applied to the determination of the triazines in fortified waters, an average recovery value of 90 % being obtained.