We report subarcsecond images of the high-mass star forming region Onsala 1 ( ON 1 ) made with the Submillimeter Array ( SMA ) at 0.85 mm and the Very Large Array at 1.3 cm and 3.6 cm . ON 1 is one of the smallest ultracompact H II regions in the Galaxy and exhibits various star formation signposts . With our VLA and SMA observations , two new cm-wave sources and five sub-mm dust sources , respectively , within a field of \sim 5 \arcsec ( corresponding to a linear scale of 0.05 pc ) are identified , indicating the multiplicity at the center of the ON 1 region . The dust and gas masses of these sub-mm sources are in the range of 0.8 to 6.4 M _ { \sun } . Among the five sub-mm dust sources , SMA2 , with a dust and gas mass of 2.6 M _ { \sun } , demonstrates several star formation signatures , and hence likely represents an intermediate-mass ( or even high-mass ) star forming core . Due to the low star formation efficiency of \sim 10 % , we suggest that star formation in the ON 1 region will continue . For example , SMA4 and SMA5 are not associated with any star formation signatures and likely mark star formation cores at very early evolutionary stages .