A voltage regulator with adaptive hysteretic control. The voltage regulator may include a top switch (e.g., MOSFET) configured to couple a power supply supplying an input voltage to a load. An adaptive hysteretic control circuit of the voltage regulator may turn on the top switch when the feedback voltage reaches the low threshold and turn off the top switch when the feedback voltage reaches the high threshold. The adaptive hysteretic control circuit may adjust the upper and lower threshold to make the voltage regulator working like a constant on time control circuit in steady state. When a step down transient happens, the top switch could be turned off when the output voltage reaches the upper threshold, and when a step up transient happens, the top switch could be turned on when the output voltage reaches the lower threshold, it makes the voltage regulator working like a hysteretic control circuit.