The mechanical behavior of a two-dimensional structure with negative Poisson`s ratio (auxetic structure) was experimentally studied. The concave hexagon (re-entrant honeycomb) with straight sides is often an element of auxetic structures. In this paper, a new design of a concave hexagon in which a part of straight elements is replaced with curvilinear elements is suggested. The sample (110 × 20 × 0.7 mm plate with the central part of 26.2 × 20 × 0.7 mm) was made by the laser cutting method from nonauxetic polyethyleneterephthalate (PET-a amorphous) plates. The transverse size of elements of hexagons is equal to sample thickness. The sample was subjected to a monotonous uniaxial tension until the last moment when it still maintained its planarity. As a result of experimental data processing the tensile force — displacement diagram was calculated. Variability of Poisson`s ratio depending on engineering deformations was studied. The analysis showed that auxetic structure at tension attained the maximum longitudinal deformation (before loss of stability) of 99 %, and the maximum transverse deformation of 59 %. Elastic deformations reached 2 %. Poisson`s ratio defined by analogy with elastic small deformations varies in the range from –0.19 to –0.60 with an increase of longitudinal and transverse deformations.