This paper presents a dual-band (DB) high efficiency power amplifier (PA) with two adjustable transmission zeros (TZs). The parallel Two Section Transmission Line (TSTL) is introduced in the impedance matching network (IMN), generating adjustable TZs and compensating for the resulting unrelated difference of admittance at DB fundamentals, which enables the DB IMN exhibits adjustable TZs out-of-band. The matching bandwidth of the DB IMN is further analyzed to seek the target impedance for broadband DB matching. The series TSTL is employed to modulate the target impedance to the impedance of the drain at DB fundamentals while satisfying the high efficiency operating conditions at DB harmonics. For validation, a DB PA is designed and fabricated with a Cree CGH40010F GaN transistor. The fabricated DB PA features the saturated output power of 42.6dBm and 42.0dBm with the Power-Added Efficiency (PAE) of 66.1% and 67.8% at 0.9GHz and 2.4GHz, respectively. Specially, the bandwidth of the DB PA is 150MHz, and two adjustable TZs are shown out-of-band.