A real-time exposure dose control algorithm for deep ultraviolet (DUV) excimer lasers in a step-andscan optical lithography is presented. By establishing an abstract scan exposure model and analyzing the pulse-topulse energy fluctuation characteristics of DUV excimer lasers, a real-time dose regulation is implemented based on closed-loop feedback control, which especially focuses on reducing the effect of pulse energy overshot and pulseto-pulse stochastic fluctuation. The experiment conducted on an ArF excimer laser with wavelength of 193 nm, repetition rate of 4 kHz, and pulse energy of 5 mJ confirms that such a real-time dose control algorithm is able to achieve a dose accuracy of above 0.89% even with only 20 pulses. It is fully expected that this algorithm will not only meet increasingly stringent dose accuracy requirements for sub-half-micron lithography, but also be helpful to improve lithography throughput as well as efficiency.