We present our first experience of using superb microvascular imaging (SMI) with an 18-MHz linear probe to diagnose placenta accreta spectrum (PAS) in the retained placenta after vaginal delivery. In the first case, irregular minimal invasion of the retained placenta into the anterior myometrium and a thin uterine wall were clearly noted. In the second case, SMI clearly demonstrated the loss of myometrium anterior to fundal lesions and abnormally dilated, torturous, stem villous vessels invading until the uterine serosa. SMI with the use of an 18-MHz linear probe may be a novel diagnostic tool for the diagnosis of PAS in the retained placenta after delivery.