Weshshiembet Girma, 29, and Muluemebet Girma, 21, of separate addresses in south London, were charged with failing to disclose information that could have helped police secure the arrest, prosecution or conviction of a person involved in terrorism, a Metropolitan Police spokeswoman said.
Press Association reported that the women are sisters and that both were arrested on July 27, accused of failing to disclose the required information between July 21 and July 28.
They are the second and third persons to be charged in Britain in connection with the failed July 21 bombings on London's subways.
The first person charged, Ismael Abdurahman, 23, from southeast London, appeared in court Thursday to face charges of withholding information that helped suspected subway bomber Hamdi Issac avoid capture.
London police are continuing to detain 12 other suspects without charge.
Police say that in the week after the attack, Abdurahman had information he knew might help police capture suspects involved in "the commission, preparation or instigation of an act of terrorism."
He was charged under antiterrorism legislation and is to attend a hearing in London on Thursday.
The charges could mark an important step forward for police seeking to build cases against the 17 people in custody in connection with the July 21 assault, in which bombs planted on three subways and a bus failed to fully detonate.
Police also are trying to uncover the larger network that may have supported those attackers, who struck exactly two weeks after four suicide bombers, also on three trains and a bus, and killed 52 victims on July 7.
One of the suspected July 21 bombers, Hamdi Issac, has been charged in Italy with association with the aim of international terrorism. Britain is seeking to extradite him. Italy also has two of Issac's brothers in custody, and Britain is holding 14 suspects.
No suspects are being detained in connection with the July 7 attacks.