Some previous studies suggested that diet can impact the B vitamin content of cow milk. So, milk B vitamin concentrations from cows at pasture could be different from cows fed indoor. Four homogeneous groups of 10 cows, differing according to the proportion of grazed grass in the ration were conducted during the spring-summer period. Two groups had grazed grass as main forage whereas it was corn silage for the 2 other groups. Inside each forage group, a reduction of grass availability, simulating a drought hazard, was performed during the last 2 months. Concentrations of milk vitamins B1, B2, B5, B6 (pyridoxine, pyridoxal, pyridoxamine), B9 and B12 were determined in tank milks collected repeatedly from each group at the end of the experimental period, in September. We observed that the milk was richer in vitamin B2 and B9 but poorer in vitamin B1 and B5 when cows had grazed grass as main forage. Drought decreased milk vitamin B2 but increased B5. Surprisingly, vitamin B12 content was the highest in the milk of cows fed corn silage and having access to pasture for a small time of the day whereas it was the lowest when the access to pasture was fully removed.