A field experiment was conducted at Department of Horticulture, College of Agriculture, Rajmata Vijayaraje Scindia Krishi Vishwa Vidyalaya, Gwalior, (M.P.) during rabi 2014-15 and 2015-16 to study the effect of gibberellic acid and Trichoderma viride on growth and yield of onion (Allium cepa L.) cv. Agrifound Light Red. Foliar application of GA3 100 mg and soil treatment of T. viride (10 kg ha-1) (T11) was observed significantly maximum (68.67, 64.53 and 66.60 cm) plant height, (18.67, 16.97 and 17.82) number of leaves plant-1, (62.83, 59.50 and 61.17 cm) length of leaf and (1.14, 1.12 and 1.10 cm) width of leaf at first year, second year and pooled, respectively, over to control (T1 i.e., GA3 0 mg + T. viride 0). Growth analytical parameters viz., (668.47, 556.97 and 612.72 cm2) leaf area plant-1, (4.46, 3.71 and 4.09) leaf area index, (1.77, 1.71 and 1.74) bulb /green top ratio and (1.49, 1.46 and 1.48) neck thickness of bulb at first year, second year and pooled, respectively, over to control (T1 i.e., GA3 0 mg + T. viride 0). Significantly maximum (44.43, 42.18 and 43.31 g) fresh weight of bulb plant-1 and (28.13, 28.07 and 28.10 g) dry weight of bulb per 100g fresh weight.(5.36, 5.31 and 5.33 cm) diameter of bulb, (5.11, 5.90 and 6.01 cm) length of bulb and (329.94, 323.57 and 326.76 q ha-1) bulb yield were recorded in the treatment T11 (GA3 100 mg and soil treatment of T. viride (10 kg ha-1) at 1st year, second year and pooled, respectively. Significantly maximum (16.04, 15.73 and 15.89 kg plot-1) and (329.94, 323.57 and 326.76 q ha-1) bulb yield were recorded in the treatment T11 (GA3 100 mg and soil treatment of T. viride (10 kg ha-1) and lowest (0.10, 0.07 and 0.09%) bolting percentage and this treatment also proved the best antagonistic activity against Fusarium oxysporu sp. cepae basal rot with minimum disease incidence (5.22, 5.20 and 5.21 %) over to control at 1st year, second year and pooled, respectively.