A method based on microchip electrophoresis with electrochemical detection has been developed for the simultaneous determination at trace levels of the main small-chain aldehydes (formaldehyde, acetaldehyde and 2-propenal) present in the atmosphere. Sampling was performed by forcing atmospheres through silica-gel cartridges coated with 2,4-dinitrophenylhydrazine (DNPH), where aldehydes were derivatized to form the corresponding hydrazones, which were then injected and eluted into the electrophoresis system. Factors affecting both separation and detection processes were optimized, with best performance achieved by applying a voltage of 2500V both in the separation and in the electrokinetic injection (5 s) and using a 15 mM borate buffer (pH 9.2) added with 25 mM of SDS and 20%v/v ACN plus 10%v/v 1-propanol. Under these optimal conditions, well satisfactory resolution could be achieved, so that the analytes could be separated and detected within about 400 s, by applying a detection potential of -1.0 V versus Ag/Ag/Cl to the glassy carbon-working electrode. The recorded peaks were characterized by both a good repeatibility (RSD < 3%) and a linear dependence over a wide concentration range (2-100 mu g/mL). Detection limits, estimated for a SIN of 3, equal to 9.5, 7.2 and 9.2 mu M were inferred for the DNPH derivatives of formaldehyde, acetaldehyde, 2-propenal, respectively. The application of the method to aldehyde analysis in real air samples is also presented.