In a temperate climate the photosynthetic capacity (P_max) changes during the year. In this study we focus on the leaf anatomy and seasonal changes in photosynthetic nitrogen use efficiency (PNUE). We studied the evergreen understory shrub Aucuba japonica grown in pots under two light treatments outside for four seasons. The P_max measured at 15 degrees decreased strongly from summer to winter, with no clear sign of photoinhibition, and increased again in spring. The leaf nitrogen content increased towards winter and was correlated with the chloroplast volume and its surface area facing the intercellular space (S_c). S_c occupied 59 % in summer up to 81% in winter of the mesophyll area facing the intercellular space. So the open leaf structure in summer allowed for an increase in nitrogen in winter. The PNUE changed similar to P_max over the year. There was no change in the relation between rubisco and nitrogen over the year. The P_max per unit rubisco (P/R) changed strongly over the year with the lowest values in winter. The P/R however did not scale with the increase in chloroplast surface area. In winter the internal CO₂ diffusion seemed to be hampered by the chloroplast thickness whereas for the rest of the year the stomatal conductance affected PNUE.