Chemical characterization of suspended particulate matter (SPM) measured inside a naturally ventilated school building (indoor) and at an adjacent roadway (outdoor) in Chennai city was performed during monsoon, winter and summer seasons. The daily average indoor SPM concentrations in monsoon, winter and summer seasons were 158.18, 170.08 and 149.63μgm-3, respectively. Indoor and outdoor samples were analyzed for 11 inorganic ions using ion chromatography and 28 elements by inductively coupled plasma optical emission spectrometry. Results indicated the dominance of SO42- (10.89μgm-3) followed by NH4+ (5.62μgm-3), NO3- (5.35μgm-3), Na+ (4.35μgm-3) Ca2+ (4.08μgm-3) and Cl- (3.47μgm-3) ions in the indoor SPM. In the outdoor SPM, SO42-, NO3- and NH4+ ions concentration were slightly higher while Ca2+, K+ and Mg2+ ions concentrations were higher in indoors. Among the elements, crustal element (Al, Fe, Ca, K, Mg and Na) concentrations were much higher (92.7% of the total elemental concentration) in indoor environment than those of toxic elements (Ba, Cr, Cu, Mn, Mo, Ni, Sr, Ti, V and Zn) emitted from vehicles. Analysis of elemental carbon (EC) and organic carbon (OC) components in indoor and outdoor PM indicated the predominance of OC. The indoor/outdoor (I/O) ratios for EC=0.70 and OC=0.82, indicating no significant indoor emission sources of OC and EC. To characterize the morphology, indoor and outdoor filters were examined by Scanning Electron Microscopy coupled with energy dispersive X-ray spectrometry. Soot and Al-Si rich particles were mostly found in indoor and outdoor SPM. The presence of toxic elements and soot particles in the indoor PM confirms the contributions of vehicular emissions from the adjacent motorway. © 2013 Elsevier Ltd.