An L band (1357.5 MHz) boundary layer radar (BLR) has been in continuous successful operation in Serpong, Indonesia (6.4°S, 106.7°E), since November 1992. The performance of the BLR with respect to the observation height range and the wind measurement reliability has been examined on the basis of simultaneous meteorological observations. We have found that there are two types of strong echo structures appearing systematically in the equatorial planetary boundary layer with diurnal variations on clear days. The first type is the striking appearance of a strong echo layer ascending from below 300 m (in the morning) to above 3–5 km (in the afternoon), which is identified with a diurnal variation of the top of the mixing planetary boundary layer. As expected, it is higher in the Indonesian equatorial region than in midlatitudes. Another type is layered echoes appearing at 2–3 km heights from nighttime to morning, which seem to be coincident with humidity gaps.