We show that the size evolution of emission line objects differs substantially from continuum selected objects. While the latter show substantial evolution in size at redshifts z < 4, a magnitude limited sample of objects selected from the GRISM ACS PROGRAM FOR EXTRAGALACTIC SCIENCE (GRAPES) project, does not. The GRAPES project observed the Hubble Ultra Deep Field (HUDF) using the slitless grism spectoscopy mode of the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). We have identified 124 emission-line objects (eGRAPES), a sample complete down to a limiting AB magnitude of z = 27.6, based on the detection of emission line in the spectra of these objects. The average line flux is 10-17 erg s-1cm-2, with the faintest ones reaching 3×10-18 erg s-1cm-2. We have performed careful morphological measurements of these objects and have determined that most of these objects are very blue (B−V < 0.6), late type objects with a high effective surface brightness ( μe < 21.0 mag arcsec-2 ). These objects appear to be good candidates for Luminous Compact Blue Galaxies and offer a unique new sample of such objects over a wide redshift range.