Laccase production by Penicillium martensii NRC 345 was optimized. Eight media with different components were screened. The enzyme formed by P. martensii NRC 345 was detected mainly exocellularly under shake culture condition. Laccase formation reaches its maximum value with specific activities of about 7.18 U/mg protein at the twenty-sixth day of incubation at pH 5.5 and 30°C. Galactose (5 g/l) and sodium nitrate (0.2 g/l) were found to be the best carbon and nitrogen sources for laccase formation, respectively. Replacement of galactose instead of glucose at the same concentration increased laccase production by about more than ten-fold. Among the various wastes used wheat bran induces the highest laccase production with specific activity of 39.52 U/mg protein. Tween-80 and CuSO4.5H2O, were also tested for laccase induction.