Pébrine is the most important disease of silkworm, Bombyx mori (L.) (Lepidoptera: Bombycidae), and is caused by Nosema bombycis (Nägeli) (Dissociodihaplophasida: Nosematidae). We investigated the effect of N. bombycis infection on the total hemocyte count (THC) and the differential hemocyte count (DHC) in hemolymph of a disease-resistant line (Line 104) and a susceptible line (Line 153) reared under optimum conditions. Fifth-instar silkworms were inoculated with a microsporidia spore suspension. Hemolymph was collected on the second, fourth and sixth days after inoculation, and THC and DHC of infected and uninfected silkworms were enumerated. Significantly higher THC was observed in the infected silkworms than the uninfected silkworms, but there was no significant difference in THC between lines. A significant difference in THC among days since inoculation in both lines was observed, with the average THC being higher on the second day since inoculation. DHC were significantly different among lines and days since inoculation. Granulocytes and plasmatocytes were the most numerous in Line 104, whereas granulocytes, plasmatocytes and prohemocytes were the most numerous in Line 153. Nosema infection decreased the percentage of all hemocytes, but increased the percentage of adipohemocytes and plasmatocytes. This study contributes to an improved understanding of the effects of microporidian infection that affects the sericulture industry.