The search giant claims four patents have been violated, and has filed cases against the firm in California and London. It is the first time Google has launched a case against another company over patents.
BT and Google are already involved in a legal dispute launched by BP in 2011, which has yet to be resolved.
“We have always seen litigation as a last resort, and we work hard to avoid lawsuits,” said a spokeswoman for Google. “But BT has brought several meritless patent claims against Google and our customers - and they've also been arming patent trolls.”
“Patent trolls” are firms that acquire patents in order to extract settlements for infringements at a later date.
BT said it would not comment on the case.