Laminar flame speeds and Markstein lengths of tert-butanol-air premixed mixtures were measured over a wide range of equivalence ratios at different initial temperatures and pressures by using the spherically propagating flame in a constant volume combustion chamber. Effects of Markstein number, flame thickness and density ratio at two sides of flame front on flame instability were analyzed combined with the schlieren photos. Results show that the unstretched flame propagation speeds and laminar flame speeds of the tert-butanol-air mixtures increase with the increase of initial temperature and decrease with the increase of initial pressure. Peak values of laminar flame speeds present at equivalence ratio of 1.1 regardless of initial pressure and temperature. Markstein length decreases with the increase of initial pressure. Flame front instability increases as equivalence ratio and initial pressure increase. Cellular structure appears at elevated pressure. The combined effect of diffusional-thermal instability and hydrodynamic instability leads to the increase of flame instability as initial pressure increases. (C) 2011 Elsevier Ltd. All rights reserved.