Two long-term fertilization trials were established in 1966 on a Calc(ar)i-Epihypogleyic Luvisol at LUA Experimental station (Kaunas district). Experimental data of the period 2004 – 2005 presented in the paper shows the impact of long-term fertilization of mineral and organic fertilizers, its combinations on soil biological activity. Experimental data shows that the influence of various rates of fertilizers and their combinations on enzyme activity and respiration intensity was different. Hydrolases - urease and sacharase - activity more influenced by using mineral fertilizers, whereas oxidoreductases – dehydrogenases – activity more influenced by using mineral and organic fertilizers. Mineral fertilizers increased urease activity by on average 12 percent, whereas sacharase activity was not influenced, compared with unfertilized. The application of organic and mineral fertilizers increased activity of thus enzymes, accordingly 33 and 7 percent. In the second trial, treated with organic and mineral fertilizers, dehydrogenase activity was significantly influenced by application only rate of and 100 t ha-1 of manure per crop rotation. Under application of only mineral fertilization dehydrogenase activity in soil increased, compared with unfertilized. Average data of two years investigations under application of mineral – organic fertilizers and its combinations show that soil respiration intensity was significantly influenced by application only rate of N100P60K60. Key... [to full text]