Abstract. The high beta confinement and stability of a reversed field pinch (RFP) of a small aspect ratio is studied theoretically. The small aspect ratio RFP is attractive for realizing the quasi-single helicity state with improved confinement and a high bootstrap current fraction, and is planned for a new experiment at AIST Japan. Here the equilibrium profile and accessible beta value of a small aspect ratio RFP plasma are calculated. The Mercier stable beta limit of RFP plasma is roughly proportional to A. A relatively low beta nature of small aspect ratio plasma is significantly improved by an edge current modification. The beta value of 0.2 is stable at A=2. The effect of bootstrap current is also evaluated and discussed by solving a self-consistent neoclassical MHD equilibrium equation. The generated bootstrap current increases substantially the local and global magnetic shears and a higher beta limit is expected. These equilibrium and stability databases may support strongly both the mode control and high beta confinement, and also an economic and compact reactor core concept of a small aspect ratio RFP.