A field experiment was conducted during Kharif 2012 at Khrindwa research farm of CCS Haryana Agricultural University, Regional Research Station, Karnal, under the Bio-safety Research Trial Level-1 for transgenic maize hybrids to evaluate the bio-efficacy of glyphosate as post-emergence herbicide against weeds. There were 14 treatment combinations, including two transgenic hybrids of Monsanto, Hishell-NK603 and 900M Gold-NK603. Weed flora of the field included Echinochloa crus-galli, Dactyloctenium aegyptium, Brachiaria reptans and Eragrostis tenella among grassy weeds, Physalis minima and Phyllanthus niruri among broadleaf weeds and Cyperus rotundus among sedges along with few other minor weeds. Use of glyphosate 900-1800 g/ha in transgenic maize hybrids Hishell-NK603 and 900M Gold-NK603, provided 98.2-99.5% weed control efficiency, which was higher than the atrazine 750 g/ha treatments (62.1-68.6%); and resulted in improved grain yield of maize (7.7-8.7 t/ha) than unweeded checks (4.7-5.9 t/ha) and atrazine treatments (5.8-7.5 t/ha). At 60 DAT, minimum weed population (8.0-9.3/m2) was recorded in the glyphosate treatment at both the doses in transgenic maize hybrids, which was significantly lower than the atrazine treatments (19.3-21.3/m2) in transgenic/ conventional hybrids, as well as the non-weeded (37.3-41.3/m2) checks in conventional hybrids. Glyphosate 900-1800 g/ha in 900M Gold-NK603 produced maximum grain yield (8.6-8.7 t/ha) which was followed by glyphosate 900-1800 g/ha in Hishell-NK603 (7.7-7.8 t/ha). The growth, yield and yield attributes indicated superiority of 900M Gold-NK603 over Hishell-NK603, however, the differences in yield were not significant. Present study indicated the suitability of glyphosate use as post-emergence in transgenic maize hybrids Hishell-NK603 and 900M Gold-NK603. There was no phyto-toxicity of glyphosate 900-1800 g/ha on the transgenic crop.