The microwave spectra of the ammonia-diacetylene and water-diacetylene complexes have been observed with a pulsed-beam, Fabry-Perot cavity, Fourier-transform microwave spectrometer. In addition to the normal isotopic forms, we have also observed the spectra of ND3HCCCCH, 15NH3HCCCCH, HDOHCCCCH, and D2OHCCCCH. Rotational analyses of NH3HCCCCH, ND3HCCCCH, and 15NH3HCCCCH provide the rotational constants B = 1067.83088(14) MHz, 959.96176(31) MHz, and 1035.49151(13) MHz, respectively. The observed spectra are consistent with an axially symmetric complex where the diacetylene hydrogen bonds to the nitrogen of ammonia with a hydrogen-bond length of 2.29 Å. The electric dipole moment is determined to be 2.3188(21) D. For the water-diacetylene complex, the rotational constants are B = 1065.45177(18) MHz and C = 1062.03011(18) MHz for H2OHCCCCH, (B + C) 2 = 1023.98908(11) MHz for HDOHCCCCH, and B = 990.81650(31) MHz and C = 985.39905(31) MHz for D2OHCCCCH, respectively. Stark effect measurements for H2OHCCCCH give a dipole moment of 2.2971(16) D. The most probable structure of H2OHCCCCH is C2v planar with diacetylene hydrogen bonded to the oxygen of the water. The hydrogen-bond length is calculated to be 2.20 Å. Present results derived for the diacetylene complexes are compared with those of the acetylene complexes. It is noteworthy that the induced dipole moment of the ammonia-diacetylene complex is about 50% larger than that of the ammonia-acetylene complex. The effects of the conjugation of the carbon-carbon triple bonds are discussed. © 1990.