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The annual variation in planetary boundary layer (PBL) height is determined from the profiles of conserved thermodynamic variables, i.e., virtual potential temperature theta (v) and equivalent potential temperature theta (e), using radiosonde data at per-humid climate region, Ranchi (23A degrees 42’N, 85A degrees 33’E, 610 m asl) and semi-arid region, Anand (23A degrees 35’N, 72A degrees 55’E, 45.1 m asl), India. Of all the variables, the theta (v) profile seems to provide the most reasonable estimate of the PBL height. This has been supplemented by T-Phi gram analysis for specific days. It has been found that in winter the height of boundary layer is very low due to subsidence and radiational cooling, while pre-monsoon months exhibit the most variable convection. It may be inferred that synoptic conditions accompanied by a variety of weather phenomena such as thunderstorms, onset and withdrawal of monsoons, etc. control the ABL over Ranchi, while daytime solar insolation and nighttime radiative cooling mainly control the ABL over Anand.