For melt-compounded poly(caprolactone) (PCL) containing precipitated calcium carbonate (PCC) having high weight fractions Wpcc added up to 40 wt%, this study examined rheological and mechanical properties of PCC filled composites, with a focus being particularly placed on formation of PCC network structure in the Wpcc range between 30 and 40 wt%. For the composites containing Wpcc = 30 wt%, the linear viscoelastic measurements revealed only a marginal increase in low-frequency storage G’ and loss moduli G” in comparison with those of the neat PCL matrix due only to filler effect of PCC. However, as Wpcc increased from 30 to 40 wt%, there were drastic increases in both low-frequency G’ and G”, exhibiting a liquid-solid transition resulted from the formation of the PCC network structure. This formation of the network structure was also observed from a scanning electron microscopy in which the image of Wpcc = 40 wt% revealed an interconnected PCC network. The PCC network formed in the composite having Wpcc = 40 wt% significantly enhanced the ultimate tensile strength and Young’s modulus by 127.4 and 292.8 %, respectively, compared with those of the neat PCL matrix. In contrast, for the composite having Wpcc = 30 wt%, those changes in the mechanical properties were less significant (the tensile strength and the modulus were only increased by 117.7 and 163.8 %, respectively compared to the neat PCL matrix). The elongation at break was, however, decreased gradually to Wpcc = 30 wt%, and dropped suddenly with Wpcc = 40 wt%.