Dry rot of potatoes is caused by several fungal species in the genus Fusarium, of which Fusarium solani is an outstanding cause of postharvest potato losses globally. The fungus can also cause a broad spectrum of infections in humans and animals. The dry rot disease spread in the potato field has been treated mainly using fungicides that are very harmful to human health. The use of fungicides also pollutes the living environment and unbalances the microbial ecosystems in nature. Streptomyces flaveus has been known to produce antibiotic SW-B capable of inhibiting the growth of several plant pathogenic fungi. However, it has not been clear whether S. flaveus is able to inhibit the growth of F. solani. This study isolated the fungus that caused the potato dry rot from the diseased potato tubers and evaluated the antifungal activity of S. flaveus against the isolated fungus. Cell morphology and phylogenetic analyses of the fungus showed that F. solani was successfully isolated. It was found that this fungal isolate was sensitive to S. flaveus. This actinomycete produced extracellular chitinase whose concentration in the liquid culture was affected by the supplementation of colloidal chitin and fungal cell powder into the culture medium, making the F. solani mycelial cell an important factor for optimizing chitinase concentration in biocontrol preparation for prevention and treatment of the dry rot disease in potato tubers.