vi ~/.gtkrc-2.0
写入如下内容设置自己想要的字体大小

style "imhtml-fix"
{
    font_name = "Sans 14"
}

widget "*pidgin_conv_entry" style "imhtml-fix"
widget "*pidgin_conv_imhtml" style "imhtml-fix"
widget "*pidgin_log_imhtml" style "imhtml-fix"
widget "*pidgin_request_imhtml" style "imhtml-fix"
widget "*pidgin_notify_imhtml" style "imhtml-fix"