We describe a new instrumental technique for the excitation, acquisition, and analysis of fluorescence decays from a variety of substances, in the present case plastic scintillators. The fluorescence is excited by β particles from a radioactive source (100 μCi Sr-90). A random photon from the resulting fluorescence decay provides a trigger pulse to start a time-to-amplitude converter (TAC), while another random photon from the same β-excitation event provides the stop pulse. The optical components and geometry for detecting these two photons, i.e., the two photomultipliers (PMT), the filters, and the pulse counting system, are identical. As a consequence, the measured fluorescence signal is the autocorrelation function of the fluorescence decay from the sample. A delay line of 50 ns is inserted between the “stop” signal PMT and the TAC so that those “stop” pulses which arrive before “start pulses” also are recorded. Thus the acquired fluorescence signal versus time is symmetric about the delay time and contains twice as many counts as without delay. We call the new technique the “time-autocorrelated two-photon counting technique” (TATPC) in distinction to the conventional “time-correlated single-photon counting technique” (TCSPC). We compared both techniques with the same equipment and scintillators, where in the TCSPC case, a β particle is used for the start of the TAC instead of a random photon in the TATPC technique. We find that under similar experimental circumstances, the signal count rate with TATPC is about 50 times larger than with TCSPC. The new method is well suited for obtaining fluorescence decay times from plastic scintillators, which we use in this article to exemplify the technique. More generally, β-particle excitation in combination with TATPC should prove useful for materials with high energy levels or band gaps, which cannot be excited with pulsed lasers in the visible region. The length of our excitation pulse is less than 20 ps and is negligible compared to the temporal response of about 1 ns of the rest of the apparatus. By employing mathematical deconvolution, we are able to measure fluorescence decays from the subnanosecond range and to longer times.