Abstract: An anti-leakage device in a fan mainly includes a blade assembly, a fan base and a motor section. The fan base is provided with a plurality of lock holes at the bottom of the spindle seat with an oil cap being pressed into a hollow space of the spindle seat of the fan base and a plurality of engaging juts are provided on the oil cap to engage with the lock holes of the spindle seat with an oil ring being placed between the spindle seat and the oil cap. The anti-leakage device has a tight engagement structure to perform prevention of the lubrication oil leakage and the bearing seat and the spindle in the blade hub constitute a joint with a slant angle and an oil resistant groove to avoid the lubrication oil leaking outward the fan via the spindle and the bearing seat.