The Rondonia Boundary Layer Experiment (RBLE-Ⅱ) was conceived to collect data the atmospheric boundary layer over two representative surfaces in the Amazon region of Brazil; tropical forest and a deforested, pasture area. The present study deals with the observations of atmospheric boundary layer growth and decay. Although the atmospheric boundary layer measurements made in RBLE-Ⅱ were not made simultaneously over the two different surface types, some insights can be gained from analysing and comparing with their structure. The greater depth of the nocturnal boundary layer at the forest site may be due to the influence of mechanical turbulence. The pasture site is aerodynamically smoother and so the downward turbulent diffusion will be much less, resulting in a lower surface temperature. The strength of thermal inversion is, consequently, higher over the pasture than over the forest. The development of the convective boundary layer is stronger over the pasture than over the forest. The influence of the sensible heat flux is important but may be not enough to explain the difference completely. It seems that energy advection may occur from the wet and colder (forest) to the dry and warmer area (pasture), rapidly breaking up the nocturnal inversion. Such advection can explain the abrupt growth of the convective boundary layer at the pasture site during the early morning.