It is known that fracture toughness value is affected by test temperature, specimen thickness and loading rate. In the present study, specimen size and test temperature are varied widely with the obtained data then being analyzed using rate parameter. Additionally, the fracture toughness values are obtained using round bar-type specimen with a circular notch. This result is compared with the result of the CT specimens, and the advantage of using the round bar-type specimen with a circular notch to modify specimen size requirement is discussed. Sample material used is HT780 high tensile strength steel. The test specimens were 1T, 2T and 4T-CT that are described in ASTM E399. Notched round bar-type specimen with a diameter of 15mm and notch root radius of 0.25mm is also used. The test temperature is varied from a low temperature to room temperature, and loading rate is varied about the 1T-CT specimen and the notched round bar-type specimen between static and 1000mm/sec. The test temperature and the loading rate dependency of the fracture toughness values were arranged by the rate parameter. The fracture toughness value has decreased with the decrease in test temperature and with the increase in specimen thickness and loading rate. The fracture toughness value obtained from the notched round bar-type specimen indicated a value close to 2T-CT specimen. It is shown that valid fracture toughness value can be obtained with a small test specimen by the notched round bar-type specimen. The test temperature and the loading rate dependency of the fracture toughness values can be successfully arranged by the rate parameter that can express both temperature and strain rate dependencies. Feasibility of using round bar-type specimen to obtain valid fracture toughness values with less specimen mass was demonstrated.