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, 25 m³/feddan (feddan = 4200 m²) and half of the recommended doses of NPK fertilizer and microbial inoculation (Pseudomonas monteilii (MA-5) and Pseudomonas fluorescens (MP-4)) either alone or in combination, as well as, their interactions on plant growth, yield characteristics and volatile oil production of dill (Anethum graveolens L.) plants. The obtained results showed that the use of bio straw at all levels and NPK_HR, expect for the low level of bio straw in some cases led to a significant increase in plant height, number of branches/plant, weight of fresh and dry herbs g/plant, number of umbels/plant, fruit yield g/plant and kg/feddan and the percentage of volatile oil and volatile oil yield ml/plant and liter/fed. The application of a high level of bio straw (25 m³/feddan.) gave the highest values of these traits. Apparently, application of microbial inoculation by MA-5 or MP-4 alone particularly MA-5 resulted no effect significant in the studied parameters, in most cases, in contrary, the mixture inoculation (P monteilii and P fluorescents) significantly augmented all growth attributes. The highest values of these parameters were detected when inoculation in most cases 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 all parameters. The addition of the high rate of bio straw plus inoculation mixed of bacteria was the most effective treatment in increasing these aspects.