The report said DoCoMo's income fell to 163.5 billion yen ($1.41 billion) in the April-June period, the company's fiscal first quarter, compared with 207.9 billion yen ($1.8 billion) a year earlier, according to a statement from the Tokyo-based company.
Sales rose 2.7% to 1.22 trillion yen ($10.5 billion) from 1.19 trillion yen ($10.3 billion), the report said.
Competition to win customers in Japan's cutthroat cell phone market had been intense despite the ballooning costs to develop new mobile technologies. Handset prices declined quickly, making it difficult for companies to make profits, the report said.
The report further said first-quarter profit at DoCoMo was partly eroded by a 46.4-billion-yen ($400-million) increase in operating expenses in the period, more than 60% of which were related to selling new handsets.