A modular frame structure of a partition wall made of panes of glass or a similar material, or made of panels of plasterboard or a similar material, comprising - a side assembly to form at least one of the lower side, or base, of the frame structure , or the upper side, or cross bar, of the frame structure ; - said side assembly comprising - a track suitable to firmly connect to the ceiling or the floor or a support structure, said track having a body extending along a preset first longitudinal extent (X-X); - said assembly further comprising a section bar which is telescopically connected to said track ; - a coupling section bar suitable to be secured to said pane ; - said telescopic section bar forming at least one invitation and coupling seat receiving said coupling section bar ; - said invitation and coupling seat being defined by a sliding and resting wall that with an edge thereof defines a seat opening through which the coupling seat opens to the outside of said telescopic section bar ; - said assembly further comprises a snap-coupling device ; - said invitation and coupling seat being defined by a bottom wall ; said modular frame structure being characterized in that said invitation and coupling seat comprises a snap-coupling device seat , in which said snap-coupling device is received with a base portion thereof so that a body portion thereof projects cantilever in said invitation and coupling seat and, facing said sliding and resting wall , forms therewith a coupling slit that, in disengaging conditions, has reduced dimensions going towards said seat opening ; - said body portion of said snap-coupling device having a shape and a material allowing an elastic deformation thereof to snap-receive said coupling section bar in said coupling slit so that an undercut provided for in said coupling section bar is coupled by the mutual action of the snap-coupling device and the sliding and resting wall . - a side assembly to form at least one of the lower side, or base, of the frame structure , or the upper side, or cross bar, of the frame structure ; - said side assembly comprising - a track suitable to firmly connect to the ceiling or the floor or a support structure, said track having a body extending along a preset first longitudinal extent (X-X); - said assembly further comprising a section bar which is telescopically connected to said track ; - a coupling section bar suitable to be secured to said pane ; - said telescopic section bar forming at least one invitation and coupling seat receiving said coupling section bar ; - said invitation and coupling seat being defined by a sliding and resting wall that with an edge thereof defines a seat opening through which the coupling seat opens to the outside of said telescopic section bar ; - said assembly further comprises a snap-coupling device ; - said invitation and coupling seat being defined by a bottom wall ; - said body portion of said snap-coupling device having a shape and a material allowing an elastic deformation thereof to snap-receive said coupling section bar in said coupling slit so that an undercut provided for in said coupling section bar is coupled by the mutual action of the snap-coupling device and the sliding and resting wall . <EOS>