Transient behaviors of a compressed electrorheological (ER) fluid based on zeolite and silicone oil have been experimentally investigated. The ER fluid is purely compressed between two parallel plates. Compressive speed and voltage amplitude effects on the transient process and randomly applied on/off voltages have been studied. Through normalizing compressive stress of the ER fluid, the characteristic compressive strain and the response time constant corresponding to the rise of compressive stress have been fitted with exponential equations. Results show that the rising time of the transient compressive stress is greatly affected by the compressive speed and the compressive strain position applying voltages, while the amplitude of the applied voltage has little effect on the rising time. The obtained transient compressive strain for the compressive stress to rise to its stable value is much smaller than that working in the transient process of ER fluids under shearing. The decay time and decay strain of compressive stress are much less than for stress rising. The half decay compressive strain is as small as 0.0003 in the experiment. Results show that the response time of compressed ER fluids is quick enough for the usual working conditions of squeezing ER dampers.