@Aahi You don't have to use this old connection style. Remove SIGNAL and SLOT words. auto window2 = new MainWindow(); connect(ui->pushButton, &QPushButton::pressed, window2, &MainWindow::some_slot_that_you_have_in_MainWindow_class); some_slot_that_you_have_in_MainWindow_class() { ui->checkBox->setChecked(false); } Something like that