Abstract.A double-laser beam lidar to measure potassium (K) layer at Beijing (40.5° N, 116.2° E) was successfully developed in 2010. The parameters of sporadic K s layers and their distributions were given. The seasonal distribution of K s occurrence frequency was obtained, with two maxima in July and January. The seasonal distributions of sporadic E s layer occurrence frequency over Beijing differ from those of K s . However, the good correlation between E s and K s in the case-by-case studies supports the mechanism of neutralization of metal ions in a descending E s layer.