About 75% of the tea fields in Japan grow cv. ‘Yabukita,’ which is susceptible to many diseases such as anthracnose and gray blight. Therefore, broad range effective and long-lasting disease control methods are required. Plant activators (PAs) are compounds that induce disease resistance in plants. In the present study, we used AGREVO EX (a yeast extract preparation), probenazole, prohydrojasmon, and tiadinil as PAs and estimated their disease resistance-inducing activity on tea plants by wound-inoculation assays and field trials. An aqueous solution of each PA was sprayed on field-grown ‘Yabukita’. PA-treated leaves were harvested and assayed for disease resistance-inducing activity. Lesion development of gray blight and anthracnose in PA-treated leaves was suppressed by each PA, and the induced resistance continued for at least 30 days after PA treatment. All the tested PAs induced disease resistance in tea plants systemically. In field trials, PAs were effective to the diseases of anthracnose and gray blight with control efficacies from 50.1 to 50.8 and 63.7 to 69.8 respectively. The growth and chemical composition of tea shoots were not changed by PA treatment. Based on these experiments, induced resistance by PAs is useful for the development of new disease control methods for tea production.