In order to determine the biological parameters of the burrowing crayfish (Parastacus pugnax), we fenced in 900 m² of a humid, low-lying sector in Tiuquilemu, Bío-Bío Region, Chile. Monthly samples were taken from August 2007 to August 2008, and 3,512 specimens were caught. Records were made of their carapace length (CL), total weight (TW), sex, and number of eggs (for females). The monthly size-structures showed few juveniles between 20 and 30 mm CL in nearly all months. P. pugnax was found to carry eggs from mid-spring through late autumn; size at first maturity for females was 38.1 mm CL; and fecundity varied between three and 45 eggs per female. In terms of the global sexual proportion, males were predominant in 11 of the 12 months, although the ratio was as expected (1:1). We estimated the parameters of the growth curve using modal progression analysis, obtaining CL&#8734;, K, and t0 values of 55.3 mm, 0.23 mm year-1, and -0.58 years, respectively. The length-weight relationship was calculated separately for males and females, and no significant differences were found between sexes. The common parameters defining the potential function of a = 0.00052 and b = 2.98 (P < 0.05) indicated isometric increments in weight.