In the Local Group, there are several tens of dwarf galaxies, which have sub-solar metallicity. They provide us a great opportunity to constitute a basic template to study faint low-metallicity galaxies such as high-redshift galaxies. Because metallicity is an important parameter which significantly affects gas-phase and grain surface chemistry, chemical compositions of molecular clouds in low-metallicity dwarf galaxies are of great interest. To investigate the chemical composition in low-metallicity environments, we have conducted spectral line survey observation in the 3 mm band (85-116 GHz) toward low-metallicity dwarf galaxies, the Large Magellanic Cloud, IC10, and NGC6822. The lines of CCH, HCN, HCO+, HNC, CS, SO, 13CO, and 12CO have been detected. The spectral intensity patterns are found to be similar among three dwarf galaxies. Compared with Solar-metallicity environments, the chemical compositions of dwarf galaxies are characterized by deficient nitrogen-bearing molecules, as a direct effect of the lower elemental abundance of nitrogen, and abundant CCH and deficient CH3OH, as an effect of extended photon dominated regions in cloud peripheries due to the lower abundance of dust grains.