Considering that he was mentored by a card-carrying Marxist named Frank Marshall Davis, who was a Communist Party USA (CPUSA) propagandist in Chicago and Hawaii, and given his rather blatant taste for the distribution of wealth, I'd have to say yes, he is a Marxist.
In his book "Dreams From My Father”, he wrote that during his student years at Columbia, he “went to Socialist Scholars Conferences”., he befriended scumbags like the Marxist terrorist Bill Ayers, and on April 31, 2008, L. David Alinsky, Saul Alinsky's son, wrote a letter to the editor for the Boston Globe: "Obama learned his lesson well. I am proud to see that my father's model for organizing is being applied successfully beyond local community organizing to affect the Democratic campaign in 2008. It is a fine tribute to Saul Alinsky as we approach his 100th birthday.”
There are many other instances that connect him to Marxism. I won't list them here.