This year she led Barca to a treble-winning season with the club securing the Primera Iberdrola, the Champions League and the Copa de la Reina.
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There are still three matchdays left of the Primera Iberdrola season but Barca secured the title on May 9 after beating Granadilla.
Up to that point, they had not lost a game all season although this run was snapped by Atletcio Madrid on Tuesday when they lost 4-3.
"I am here to announce that this will be my last season at the club. Happiness! I'm really happy. I arrived 16 seasons ago at the age of 14 and absolutely everything that I have experienced as a Blaugrana player has made me the happiest person in the world," Losada said at a news conference on Friday.
"I know that I am lucky to be able to be here today saying goodbye to what will always be my home. Over the years, I have learned that you have to be grateful so I want to thank the club for their treatment, for understanding my situation in all these years and for respecting me as a professional during all the stages of my career.
"Thank you to the fans for all the respect and affection, especially during the last two years in which women's football is having a lot of visibility, [thank you] to the staff for everything we have been through and the work that has been behind [our success]. And finally thanks to my teammates because, as they know, wearing the armband in this club, it is a great responsibility for everything that it represents but it also represents them. I have never forgotten about it and they have been my priority above all.
"It has been the most difficult decision of my life, premeditated for many months and many tears, looking for a way to continue here. But I have to be honest with myself and with all of you. The time has come to close this stage and I will be eternally grateful. My heart will always be Blaugrana. Thank you very much and visca el barca [come on Barca]."
Losada came through La Masia and has spent most of her career with the Catalan club apart from an early move to Espanyol, a short stint with Western New York Flash and a year-and-a-half with Arsenal in the Women's Super League. There she won the league and the FA Cup.
The Spain international leaves Barca with six league titles, one Champions League title, seven Copa de la Reina titles, one Supercopa Femenina title and eight Copa Catalyunya titles.
Eduardo Fernandez-Abascal contributed reporting to this article.