The purpose of this paper is to demonstrate a method of preparation of rod-like β-Si3N4 seeds for self-reinforced silicon nitride ceramics. β-Si3N4 seeds with different size and aspect ratios have been well developed by means of heating the mixture of α-Si3N4 containing various contents of β-Si3N4 powder with certain additives at 1800°С for holding different time under 0.5MPa nitrogen gas. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed to investigate the morphology, phase transformation and secondary phase. The influence of the proportion of β-Si3N4 in the initial α-Si3N4 powder on seeds size and morphology was investigated. The uniform β-Si3N4 seeds with controllable size and aspect ratios obtained through the β-Si3N4 addition can be explained by an increased heterogeneous nucleation, and MgO was more effective for enhancing the grain growth by the decreased viscosity.