Strawberry is one of the most important vegetable crops in Egypt for exportation. This is due to the good characteristic and early appearance in market. Black root rot is a common disease in strawberry caused by a group of soil borne pathogens include Rhizoctonia solani, Fusarium solani and Macrophomina phaseolina. This disease causes economic losses in strawberry and on a wide range of other cultivated plants. Biological control is used as environmental friend alternative method in plant protection. Bioagent alone, sometimes, cannot replace effective control achieve by chemical fungicides. Therefore, this research studied how to improve or increase the effect of biocontrol agents by mixing two different bioagents together (Trichoderma harzianum with Bacillus subtilis, Trichoderma harzianum with P. fluorescens and Bacillus subtilis with P. fluorescens) or by mixing these bioagents with different antioxidants instead of using single treatment. Two different antioxidants, i.e. potassium tartrate and salicylic acid+ ascorbic acid, were used under field conditions. Results showed that all treatments led to clear significant reduction in disease incidence compare with control treatment. Mixture of T. harzianum and B. subtilis gave the highest level of plant protection and led to increase the fruit yield. T. harzianum and P. fluorescens occupied the second rank, whereas mixture of B. subtilis and P. fluorescens was the least effective one. Combination between antioxidants and different bioagents resulted in significant reduction to the disease compared with single treatment. Synergistic effect was noticed when potassium tartrate was mixed with any of the used bioagents and reduction in disease incidence combined with yield increase were recorded. Mixture of potassium tartrate and T. harzianum was the best one, followed by mixture of potassium tartrate and B. subtilis. Potassium tartrate and P. fluorescens was the least effective mixture compare with control. Laboratory analysis for treated plants showed that disease control was positively correlated with amount of free and total phenols in treated plants. Amount of protein and chlorophyll positively correlated with fruit yield.