Abstract: A built-in self adjustable arbiter physical unclonable function（PUF） is proposed to solve the problem that the responses of arbiter PUF may not be random enough. The proposed design is consisted of challenge generation module, adjustable arbiter PUF, and self-adjustment module. Firstly, specific buffers, controlled by adjustment signals, are inserted into arbiter PUF to construct the adjustable arbiter PUF. Then, the challenge generation module based on LFSR generates random challenges to test the randomness of PUF. By analyzing the randomness, the self-adjustment module automatically sets the adjustment signals to improve the randomness. The proposed PUFs are implemented in FPGA. The experimental results show that the average randomness is 50.62%, and the standard deviation of randomness is 0.5%. Compared with previous work whose standard deviation is 3.4%, the proposed PUF effectively improves the randomness.