Although the synthesis of several bis(disilenes) has already been reported, the number of reported conjugation modes between the Si=Si double bonds remains limited. Herein, we report the properties of the stable pentasila-1,4-diene 1, which was obtained from the reaction of two equivalents of disilenide 4 with dichlorodimethylsilane. The pi(Si =-Si)->pi*(Si=Si) absorption band of 1 is considerably broadened and red shifted compared to those of the corresponding monodisilene and hexasila-1,5-diene, but blue-shifted relative to those of typical tetrasila-1,3-dienes. The bathochromic shift and the broadening of the absorption band in 1 should be attributed to the homoconjugation between Si=Si double bonds through the SiMe2 unit.