The present invention relates to a Lactuca sativa seed designated 45-171 RZ, which exhibits a combination of traits including resistance to downy mildew (Bremia lactucae) races B1:1 to B1:28, CA-I, CA-IIA, CA-IIB, CA-III, CA-IV, CA-V, CA-VI, CA-VII, CA-VIII, currant-lettuce aphid (Nasonovia ribisnigri) biotype Nr:0, lettuce mosaic virus (LMV) race LMV:1, and root aphids (Pemphigus bursarius), as well as very slow bolting. The present invention also relates to a Lactuca sativa plant produced by growing the 45-171 RZ seed. The invention further relates to methods for producing the lettuce cultivar, represented by lettuce variety 45-171 RZ.