The optical limiting property of a new polyacene-based diphenyldiacetylene oligomer was investigated. The oligomer was synthesized by reaction of diphenyldiacetylene under high pressure. Toluene solutions of the oligomer contained within a quartz cell were irradiated with the pulse from a frequency-doubled Nd:YAG laser at 532 nm. At low input fluence, the transmittance of the toluene solution obeyed the Beer-Lambert law. The transmittance was constant and agreed well with that obtained by a spectrophotometer. At high input fluence, the transmittance decreased with input fluence. The oligomer had an optical limiting property. As the concentration of the oligomer increased, the threshold for optical limiting and the saturated output fluence decreased. The inverse of saturated output fluence of the oligomer was about 1/5 of that of C-60. According to the reverse saturable absorption mechanism, the following equation was obtained between the absorbance log(I-0/I) and I-0 - I; log(I-0/I) = K(I-0 - I) + A(g), where I-0 is the input fluence, I is the output fluence, K is a parameter depending on the absorption cross section and the relaxation time, and A(g) is the absorbance of the ground state.