The aim of this study was to improve feed efficiency of inefficient (INE) cows through a moderate increase in diet’s forages /concentrate ratio. We studied the effects of replacing 8.2% corn grains of the control low fiber diet (LF, 17.5% forage NDF) by 7.5% wheat straw + 0.7% soybean meal in the high fiber diet (HF, 23.4% forage NDF). Previously to the present study, the individual efficiency of 220 cows in ARO herd estimated on a low-roughage TMR. Average residual feed intake (RFI, actual DMI minus predicted DMI according to NRC 2001 equation) of ARO lactating cows was 1.5, and the inefficient cows were characterized by RFI >2.7 (20% least efficient cows). Based on this characterization, 15 pairs of INE multiparous mid-lactating Israeli Holstein dairy cows were selected and paired into 2 groups with similar performance, intake, and efficiency data and were adapted for 2 wk to the 2 dietary treatment. Traits examined during 5 wk of the experiment were: eating behavior, milk production, in vivo digestibility, and estimation of feed efficiency (RFI, ECM/DMI and energy balance). Statistical comparison between treatment analyzed by using Mixed Model with treatment, date and date × treatment as fixed effects and animal as random effect. INE cows fed the HF diet showed slower eating rate (223.1 vs 245.9 gDM/min, P < 0.01), smaller meal size (5.56 vs 5.83 kgDM, P < 0.01), longer daily eating time (245.9 vs 223.1 min/d, P < 0.01), and longer meal duration (53.0 vs 46.6 min, P < 0.01), compared with INE cows fed the LF diet. Intake of INE cows fed the HF diet was 9.1% lower (29.2 vs 32.1 kgDM/d, P < 0.01), their dry matter digestibility reduced from 65.7 to 62.2% (P < 0.01), and their ECM yield was 7.0% lower (39.8 vs 42.8 kg/d, P < 0.01), compared with the cows fed the LF diet. Feed efficiency, measured as residual feed intake, ECM/DMI and net energy captured /digestible energy intake, were improved (1.90 vs 3.18, P < 0.01; 1.36 vs 1.33, P = 0.03; and 0.495 vs 0.447, P < 0.01, respectively) in the INE cows fed the HF compared with the cows fed the LF diet. Our results thus show the potential of improving feed efficiency for milk production of INE cows by an increase in forage/concentrate ratio.