Early blight of potato (Solanum tuberosum L.) is a major important disease after late blight disease in Algeria. This study has the objective to characterize Alternaria isolates based on cultural, morphological, physiological and pathogenical characteristics. The in vitro and in situ biocontrol test using of some actinomyces strains was carried on mycelial growth and disease incidence, respectively. The results showed significant cultural and morphological characters when by these results we can identified two species of the causal agents, Alternaria solani (six isolates), and Alternaria alternata (seven isolates). The screening test showed no resistant aspects in two varieties inoculated, Arizona and Rudolph, while the biocontrol essays showed uncourageous results with important value of inhibition rates of mycelial growth (between 40 and 84%), and a remarkable reducing of damage caused by early blight on two varieties tested. These results are very important and give us a hope to protect our potato fields without using the chemical fungicides, but it needs to confirm it by the field screening in natural environmental and cultural conditions.