Humic substances have been reported to increase plant growth. A stimulating effect on the growth of legumes may improve biological nitrogen fixation in soils. The present investigation studied dry matter production, nodulation and N content in nodules of Pigeon peas [ Cajanus cajan (L.) Millsp. Variety Prabhat], Guar [Cyamopsis tetragonoloba (L.) Taub variety Santa cruz]. and Mungbean {Vigna radiata (L.) Wilczek variety VC2419], grown in sand cultures containing a fertilizer mixture and 0 to 750 mg Kg-1 of fulvic acid (FA) or humic acid (HA). The results indicated that FA and HA were capable of stimulating dry matter production in the plants. Dry weights of roots and nodules showed a tendency to increase over the control at 75 to 350 mg Kg-1 of  FA or HA. The increases in total dry matter production were statistically significant at 750 mg Kg-1 of FA or HA, and a positive correlation was noticed between increases in dry weights of shoots, roots, and nodules and FA or HA concentrations. Fewer nodules were produced by plants receiving FA and HA treatments than the control, but the nodule mass was greater with  FA and HA treatments. The N content of nodules was little affected by the treatments; although a tendency can be noticed that 75 mg Kg-1 of FA had decreased the N content in the nodules of both pigeon peas and Guar plants.