Abstract: A new type of hydrophilic-expansion paste sealants made from bentonite for buildings was developed. Three samples were made from Na-base bentonite mixed with mineral oil and paraffin wax, and the mass fraction of bentonite used is different, i.e., 60%, 65% and 70%. A testing setup was therefore developed accordingly to determine the permeability coefficient so as to work out some properties of the paste sealants under unrestrained conditions, and the results showed that the 24-hour volume expansivities are 211%, 222% and 256% with their permeability coefficients 2.86 × 10^-8, 4.15 × 10^-8 and 4.78 × 10^-8 cm/s, respectively. All samples showed favorable low-temperature flexibility, and the samples whose bentonite content is 65% or 70% have no flowability when heated at 80°C for 2 hr. XRD patterns and SEM images indicated that the bentonite in those samples are clad well by mineral oil, and the interlayer gaps of bentonite basically remain unchanged. It implies that in the samples the hydrophilic expandability of bentonite is kept up with high moldability provided. So, the sealing performance as shown by those samples has come up to the standard for the application to buildings.