A needle-holding unit for circular knitting machines, destined to be turnably mounted to a supporting structure of a circular knitting machine and having a structure basically shaped as a hollow solid of rotation formed around a central axis, the needle-holding unit being configured for turning around said central axis and for supporting a plurality of needles capable to move so as to produce a knitted fabric; the needle-holding unit having on an outer side thereof at least one working surface, wherein a plurality of needle seats placed one beside the other and arranged around said central axis is defined on the working surface; wherein the working surface has a shape as a surface of rotation obtained through the rotation of said needle seat around the central axis, and wherein the working surface is a non-cylindrical, non-conical three-dimensional surface; the needle-holding unit being characterized in that each one of said needle seats is configured for movably housing at least one portion of at least a respective needle to be actuated with an alternate motion along the respective needle seat with a motion of extraction, by which the needle is taken out with its head and with a portion of its stem above of the needle-holding unit through an upper end of the respective needle seat so as to discharge on its stem the knitted loop previously formed and/or for taking the yarn or yarns supplied on a machine feed, and with a motion of return, so as to form a new knitted loop by holding down the knitted loop previously formed; and in that each needle seat of said plurality of needle seats has a longitudinal development inclined with respect to the central axis, each needle seat being similar to a segment of a straight line and forming an angle differing from 0° with respect to a straight line parallel to said central axis and lying on a plane traversing the needle seat itself. the needle-holding unit having on an outer side thereof at least one working surface, wherein a plurality of needle seats placed one beside the other and arranged around said central axis is defined on the working surface; wherein the working surface has a shape as a surface of rotation obtained through the rotation of said needle seat around the central axis, and wherein the working surface is a non-cylindrical, non-conical three-dimensional surface; the needle-holding unit being characterized in that each one of said needle seats is configured for movably housing at least one portion of at least a respective needle to be actuated with an alternate motion along the respective needle seat with a motion of extraction, by which the needle is taken out with its head and with a portion of its stem above of the needle-holding unit through an upper end of the respective needle seat so as to discharge on its stem the knitted loop previously formed and/or for taking the yarn or yarns supplied on a machine feed, and with a motion of return, so as to form a new knitted loop by holding down the knitted loop previously formed; and in that each needle seat of said plurality of needle seats has a longitudinal development inclined with respect to the central axis, each needle seat being similar to a segment of a straight line and forming an angle differing from 0° with respect to a straight line parallel to said central axis and lying on a plane traversing the needle seat itself.