The biomechanical characteristics of leaf blades of diploid and tetraploid cultivars of perennial ryegrass (Lolium perenne), and these effects on biting behavior of sheep were investigated using 3-D loadcell in order to clarify biting strategy of sheep and the effect of biting forces on dry matter (DM) intake. Ten, 20, 30 and 40 leaf blade segments per loadcell were offered to sheep. Sheep usually grazed leaves with low biting forces (3.5-22.1 N). The number of bites per point, number of grazed leaf blades per bite and DM weight per bite increased with increasing leaf densities. Sheep used more bites in grazing leaf blades of tetraploid Prospero than those of diploid Aurora. In contrast, the number of grazed leaves per bite was lower in grazing leaf blades of Prospero than those of Aurora. The grand means of duration time per bite and time up to a peak biting force were 0.169 ± 0.005 and 0.061 ± 0.003 s, respectively. Intake efficiency (DM weight per mean biting force) as an indicator of benefit/cost ratio was not significantly different among any treatments and the grand mean was 14.4 ± 1.0 mg DM N-1. There was an apparent correlation between bending moment and mean shearing strength, suggesting that sheep may recognize biomechanical characteristics of all leaf blades prior to prehension through sensing bending strength and decide the level of creative biting force. From the number of grazed leaf blades per bite and mean shearing strength of a single leaf, mean biting forces were estimated (5.1 N in Aurora and 4.3 N in Prospero), compared with mean biting forces (5.5 ± 0.5 N in Aurora and 6.5 ± 0.4 N in Prospero) observed in grazing trial. These results suggest that sheep may break leaf blades mainly by shearing force. Journal Compilation © 2009 Japanese Society of Grassland Science.