Particulate layers of hydroxyapatite were deposited on the inner and outer surfaces of porous poly(L-lactic acid) monolith, PLLA, by using enzymatically derived ammonia as the precipitant. PLLA specimens were surface-modified with urease and were impregnated with aqueous solutions containing Ca2+, PO4 3- and urea. As ammonia was produced by hydrolysis of urea with the aid of the urease, hydroxyapatite precipitated predominantly on the surfaces of the porous PLLA. In contrast to the conventional biomimetic method or the alternate soaking method, it took shorter time period for hydroxyapatite particles to cover the surfaces of PLLA. The resultant hydroxyapatite was proved to be bone-like apatite because it had low crystallinity, contained carbonate ion in the lattice, and had a calcium-deficient composition.