J.Crew's longtime design chief Jenna Lyons is leaving the struggling apparel company, which has strung together a series of sales declines at its namesake label over the past few years.

Somsack Sikhounmuong, who is leading women's design, hsa been promoted to chief design officer.

Lyons had been with the company for 26 years. She was named president and executive creative director in 2012. She will stay with the company as a creative advisor until her contract expires in December, J.Crew said.

"It has been an absolute pleasure to work with Jenna as my trusted partner for the past 14 years," CEO Mickey Drexler said in a statement. "She has made many significant contributions to J.Crew and has built an incredibly talented team."

"It has been beyond my wildest dreams to work with such an amazing team of people at such an incredible brand and alongside Mickey — one of retail's most talented visionaries," Lyons said in a statement. "I am excited about the next chapter for J.Crew as well as the opportunity for other creative leaders within the organization to step up and take on new responsibilities

Lyons and Drexler were credited with making J.Crew a mainstay in the American shopping scene. Yet in recent years, the preppy apparel maker has struggled to get shoppers to pay up for its styles. J.Crew is often criticized for its lofty price tags when similar styles can be found elsewhere for less.

The chain is one of many retailers struggling with a high debt load tied to a leveraged buyout. TPG Capital and Leonard Green & Partners purchased the retailer for $3 billion in 2011. At the end of fiscal 2016, J. Crew has nearly $1.5 billion in long-term debt.

The company's revenue fell 3 percent to $2.4 billion last year, while comparable sales tumbled 7 percent. That was on top of an 8 percent same-store sales decline a year earlier. J.Crew reported adjusted earnings before interest, tax, depreciation and amortization of $188.5 million. That compares with $203.4 million a year earlier.

— CNBC's Courtney Reagan contributed to this report