The present invention provides 1,5- dihydro -4h- pyrazolos [3,4-D] pyrimidin-4-ones and 1,5- dihydro -4h- pyrazolos [4,3-c] pyridin-4-one formula (I) as PDE1 inhibitor and their purposes as drug, be especially used to treat neurodegenerative disorders and mental disease.La presente invención proporciona 1,5-dihidro-4H-pirazolo[3,4-d]pirimidin-4-onas y 1,5-dihidro-4H-pirazolo[4,3-c]piridin-4-onas de fórmula (I) como inhibidores de PDE1 y su uso como un medicamento, en particular para el tratamiento de trastornos neurodegenerativos y trastornos psiquiátricos.