Studies were carried out to investigate properties of anchorage failure and group effect of deformed tension bars embedded in a massive concrete block. Pull out test specimens, one or several reinforcing bars were embedded in massive concrete blocks, were used for this experiment. As the results of this experimental studies, it is found that the anchorage strength of a bar embedded with other bars at close spacing in massive concrete are decrease up to 50% compared with those of a bar embedded independently or at wide spacing with other bars. A theory to calculate the anchorage strength of bars in a group is proposed.