A field experiment was conducted during the two successive seasons of 2021/2022 and 2022/2023 at the Experimental Farm, Faculty of Agriculture, Al-Azhar University, Assiut, Egypt to examine the effect of bio  straw (spent mushroom compost "SMC") at 0, 15, 20 and 25 m³/ feddan (= 4200m²) half of the recommended doses of NPK fertilizer and Microorganisms inoculation (Streptomyces rochei [MA-6] and Bacillus subtilis [MA-13] alone or in combination, as well as, their interactions  on plant growth, yield characteristics and some active constituents of khella (Ammi visnaga L.) plants. The obtained results showed that the use of bio-straw at all levels and NPK_HR led to a significant increase in plant height, number of branches/ plant, weight of fresh and dry herbs in g/ plant, number of umbels/ plant, fruit yield in g/ plant and kg/ feddan and the percentages of khellin, visnagin and total chromones of seed khella (Ammi visnaga L.) plants. The application of a high level of bio-straw (25 m³/ feddan) gave the highest values for these above traits. Apparently, application of microorganisms' inoculation by MA-6 and MA-13 resulted a significant increase in the above parameters. The highest values of these parameters were detected by inoculation with two strains together during the two seasons. The interaction effect on all studied variables was statistically significant and it is clear that the use of most combined treatments led to a significant increase in these all parameters. Generally, the addition of the high rate of bio-straw plus inoculation mixed of two strains was the most effective treatment in increasing these parameters.