Present day high-purity Czochralski(CZ)-grown Si crystals are characterized by the bulk carrier recombination lifetime measurements. The bulk lifetime of the p-type as-grown Si with resistivity similar to 10 Omega-cm is found to be as high as 500 mu s for a CZ-Si crystal with [O-i] > 10 ppma-JEIDA and as high as similar to 1 ms or even higher for a low-oxygen CZ-Si crystal with [O-i] < 10 ppma-JEIDA. The as-grown bulk lifetime is revealed to depend not only on resistivity under the framework of the Shockley-Read-Hall (SRH) relation, but also on the oxygen concentration. The dominant recombination center of the as-grown crystal is found to be an SRH-type deep-level center which is considered to be an oxygen-related defect complex. The complex is quenched easily by a heat-treatment at a temperature as low as 650 degrees C. Effective density of a recombination center, existing after the 650 degrees C heat-treatment in the p-type crystal, correlates well with the amount of oxygen precipitation generated by a subsequent two-step heat process [800 degrees C for 4 h + 1000 degrees C for 16 h]. Thus the dominant recombination center after the 650 degrees C heat-treatment is considered to be closely related to the oxygen precipitation nuclei toward the subsequent precipitation formation heat process.