We use stellar proper motions from the TGAS catalog to study the kinematics of OB-associations .
The TGAS proper motions of OB-associations generally agree well with the Hipparcos proper motions .
The parameters of the Galactic rotation curve obtained with TGAS and Hipparcos proper motions agree within the errors .
The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 TGAS stars is \sigma _ { v } = 3.9 km s ^ { -1 } , which is considerably smaller , by a factor of 0.4 , than the velocity dispersions derived from Hipparcos data .
The effective contribution from orbital motions of binary OB-stars into the velocity dispersion \sigma _ { v } inside OB-associations is \sigma _ { b } = 1.2 km s ^ { -1 } .
The median virial and stellar masses of OB-associations are equal to 7.1 10 ^ { 5 } and 9.0 10 ^ { 3 } M _ { \odot } , respectively .
Thus OB-associations must be unbound objects provided they do not include a lot of dense gas .
The median star-formation efficiency is \epsilon = 2.1 percent .
Nearly one third of stars of OB-associations must lie outside their tidal radius .
We found that the Per OB1 and Car OB1 associations are expanding with the expansion started in a small region of 11–27 pc 7–10 Myr ago .
The average expansion velocity is 6.3 km s ^ { -1 } .