According to the most recent common data set, male enrollment = 37%. Similar numbers at Conn College. Both are former all-women’s colleges. Keep in mind that the national male:female ratio is 43:57.
A few of other factors come into play. First, there are more females than males in the population in general. Second, a higher percentage of females go onto college after high school than males. Third, a higher percentage of male college students attend public colleges than males, leaving fewer for a private college like Vassar. Finally, a vastly higher percent of engineering students are male than female (78:22). Business schools are also more heavily male than female. So, with males gravitating toward engineering and business, there are going to be that many fewer for a liberal arts college like Vassar.
Here’s a 10-year old article on the subject, but you can find current comments that say the same thing: