Vincetoxicum pycnostelma Kitag. (Apocynaceae) is a perennial herb that grows in grassland habitats in East Asia and the western part of Amur. Urbanization, land development, abandonment of traditional management of grasslands, or any combination of these factors are rapidly reducing grassland habitats, and V. pycnostelma is now ranked as a “Near Threatened” species on the Red List of Japan. Identification and characterization of pollinators of this endangered species are important in its conservation. We observed and collected insect visitors to the flowers at night and in the morning in the populations of V. pycnostelma on the banks of the Kidzu River, Kyoto, Japan from June to August in 2011. Pollinators were characterized as those insects on which flower pollinaria were attached. Twenty-seven species (9 families; 3 orders) were observed visiting the flowers; individuals of 14 lepidopteran species (6 families) had pollinaria attached to their bodies and most visited the flowers at night. Adult lepidopterans with a proboscis length of 0.9 - 4.5 mm were the primary carriers of pollinaria. Examination of stigmatic chambers of randomly selected flowers showed that the percentage of flowers in which pollinaria was inserted was much higher than the percentage of fruit set observed. Reasons for the observed low fruit set may be self-incompatibility or resource limitation. These preliminary observations were conducted at only 1 site and were restricted to a short period of time; yet, these data could be useful for elucidation of effective pollinators of this species and, thus, its conservation.