The department's Office of Civil Rights notified the university in January 2013 about a complaint alleging the university failed to adequately respond to sexual harassment reports, Washington State officials said. Those included incidents of sexual assault.
Details of the complaint were not available.
"There has been no finding of any wrongdoing on the part of WSU," the Pullman-based university said in a press release.
WSU officials said they contacted the civil rights office after receiving the complaint and asked to participate in the agency's "voluntary resolution" process, meaning the university would work with the agency to make improvements in policies and practices.
Since that time, WSU has been cooperating with the office to provide information, the school said.
In February, agency representatives visited the campus, conducting sessions with student focus groups, interviews with employees and open forums for students to meet with representatives.
"WSU takes its Title IX obligations very seriously and does not tolerate any form of sexual harassment, sexual assault, or other sexual misconduct," the school said.
Title IX prohibits gender discrimination at schools that receive federal funds. It is the same law that guarantees girls equal access to sports, but it also regulates institutions' handling of sexual violence and increasingly is being used by victims who say their schools failed to protect them.
"While we believe our complaint procedures, policies, and practices fully comply with the law, we look forward to working with OCR to make any needed improvements," the school said of the Office of Civil Rights.
Nationally, the names of the 55 schools were released two days after a White House task force promised greater government transparency on sexual assault in higher education. Going forward, the Education Department said it will keep an updated list of schools facing such an investigation and make it available upon request.
The University of Idaho in neighboring Moscow was also named.
The department previously would confirm such an investigation when asked, but students and others were often unaware of them.
Catherine E. Lhamon, the department's assistant secretary for civil rights, said a school's appearance on the list does not mean that it has violated the law but that an investigation is ongoing.
Citing research, the White House has said that one in five female students is assaulted. President Barack Obama appointed a task force of his Cabinet members to review the issue after hearing complaints about the poor treatment of campus rape victims and the hidden nature of such crimes.
The department can withhold federal funding from a school that doesn't comply with the law, but it so far has not used that power and instead has negotiated voluntary resolutions for violators.