We have investigated the spray and atomization behavior of 0.35% C934 Carbopol gels with or without 15 wt.% SUS304 nanoparticles of 100 nm using a doublet like-on-like impinging jet system (orifice diameter of 0.7 mm, impingement angle 2 theta of 90 degrees) and compared with the spray behavior of water. The spray patterns of gel materials were qualitatively different from those of water and could be divided into four types: open rim and no shedding drop; rimless sheet with ray shaped shedding; sheet with ligament separation; fully developed. The sheet sizes of water and the pure Carbopol gel increased with the increase in jet velocity, but the sheet size of the Carbopol gel containing SUS particles did not change with the increase in velocity. The aspect ratio (L-max/W-max) of the sheet was constant at 2.1 for water and 1.7 for two gel materials. Due to the high viscosity of gel materials, the amplification of sinusoidal waves was mitigated and the spreading angle was smaller when compared with water. The breakup length of the pure Carbopol gel was longer than that of water. However the breakup length of the Carbopol gel containing SUS particles was remarkably shorter than that of the pure Carbopol gel due to the increase in impact energy by the heavy particles as well as the decrease in gel strength by the addition of nanoparticles. The drop Sauter mean diameter (SMD) decreased with the increase in jet velocity, and it converged to an asymptotic value. The asymptotically convergent drop SMD of water was about 100 mu m while that of Carbopol gels was 75-77 mu m. The elasticity of gels appears to reduce the asymptotic drop size. (C). 2011 Elsevier B.V. All rights reserved.