We describe a general process, which is applicable to a wide range of materials, for transparent porous electrodes fabricated by using commercially available nanocrystalline powders. Transparent porous electrodes have potential to develop new optoelectronic devices which exchange energies between photons, electrons and molecules on large surfaces such as photoreductive/oxidative electrodes [1, 2], dye-sensitized solar cells [3–6], electrochromic [7, 8], electroluminescent devices [9], and spectroelectrochemistry [10, 11]. They consist of metal-oxide nanoparticles such as WO3 [1, 2], TiO2 [3–5, 9], SnO2 [6–8, 10–13] and are synthesized mostly by means of sol-gel coating methods. The fabrication of SnO2 and TiO2 transparent porous electrodes by means of sol-gel methods has been reported in the literature using precursors of metal-oxide ceramics, which were pyrolyzed into nanocrystals under pH-controlled conditions, followed by several complicated processes or under high temperature and high pressure using an autoclave: the so-called ‘hydrothermal synthesis [3, 4, 6, 9, 12, 13]. Without the pyrolysis of the precursor, only thin single films (<0.2 μm) have been obtained, so that the coating must be repeated several times in order to increase the thickness [7, 8]. On the other hand, porous electrodes have been fabricated by using commercially available nanoparticles but the resulting electrodes were opaque [5, 14–16]. The nanoparticles prepared by hydrothermal synthesis and the commercial powders were ground and dispersed in a polymeric solution using either an ultrasonic homogenizer [3, 4, 15], a roll-mill grinder [15], or a paint shaker [14]. The resulting paste was coated on a substrate and sintered between 450 to 550 ◦C for 30 min, giving a transparent porous electrode. With respect to WO3 an unstable precursor obtained by use of a cationexchange resin from Na2WO4 has been coated with a polymer binder and pyrolyzed to get nanoparticles, resulting in transparent porous electrodes. A commercially available H2WO4 powder was not useful for the precursor [1, 2]. As noted above, each paste for transparent porous electrodes prepared by the sol-gel synthesis needs special equipments and complicated procedures that are affected by the targeting materials. In this paper we disclose a general method to fabricate transparent porous electrodes from a wide range of materials. Moreover, our process is advantageous for using only basic and inexpensive equipment: a rotary evaporator, a hot magnetic stirrer, and an oven. This method should be especially useful for many researches and industrial applications to achieve new optoelectronic devices with transparent porous electrodes. The fabrication of transparent porous electrodes was made using inexpensive equipments available in an ordinary chemical laboratory: a rotary evaporator, a hotmagnetic stirrer, and an oven. TiO2 (F-6, Showa Titanium; diameter: d = 16 nm), Sb-doped SnO2 (SN100P, Ishihara Sangyo; d = 20 nm), and WO3 (Aldrich; d = 30 nm) were selected as commercially available powders. For the coating paste, HNO3 was adsorbed on the surface of the nanoparticles by stirring the nanoparticles in 0.1 M HNO3 aqueous solution under heating (80 ◦C for 8 hrs) and drying them in a rotary evaporator until the dispersion became powdery. The coating paste was prepared by mixing the aforementioned nanoparticles (0.8 g) in H2O (4 ml), polyethylene glycol (Mw 20000, Wako Chemical) (0.24 g) and hydroxypropyl cellulose (6–10 cps, Tokyo Kasei) (0.08 g). The stirring time was controlled between 1 to 30 days, giving a coating paste which was applied on a substrate by means of a doctor-blade technique using a glass rod [3], and then sintered at 550 ◦C for 30 min. Fig. 1a, b and c depict scanning electron micrograph (SEM) images of the surface morphologies of SnO2 films using the pastes stirred for 1, 15 and 30 days, respectively. The surface after 1 day was very rough